Bukannya saya boros, melainkan tagihan internet bulan ini naik.

This pattern means not ..., but rather ... or it’s not that ..., rather ....

So:

• Bukannya saya boros = It’s not that I’m wasteful / It’s not because I’m wasteful
• melainkan tagihan internet bulan ini naik = rather, the internet bill went up this month

The whole sentence is correcting a possible assumption. It sounds like the speaker is saying: Don’t blame my spending habits; the real reason is that the bill increased.

Because bukannya here does more than simple negation. It sets up a correction or contrast.

Compare:

• Saya tidak boros. = I’m not wasteful.
  This is just a plain statement.

• Bukannya saya boros, melainkan tagihan internet bulan ini naik. = It’s not that I’m wasteful; rather, the internet bill went up this month.
  This specifically rejects one explanation and replaces it with another.

So bukannya is useful when you want to say the problem is not X; the real explanation is Y.

Both can often be translated as but, but melainkan is more specific.

• melainkan is commonly used after a negative idea to mean but rather / instead
• tetapi just means but

In this sentence, melainkan is the best choice because the speaker is rejecting one explanation and giving the correct one.

So:

• Bukannya saya boros, melainkan tagihan internet bulan ini naik.
  = It’s not that I’m wasteful, but rather the internet bill went up this month.

Using tetapi would still be understandable in casual speech, but melainkan fits the logic more precisely.

Boros means wasteful, extravagant, or spendthrift, depending on context.

It is used for someone who uses or spends too much money, time, electricity, fuel, etc.

Examples:

• Dia boros uang. = He/She wastes money.
• Mobil ini boros bensin. = This car uses a lot of gas.

In your sentence, saya boros means I’m wasteful with money / I spend too much.

It means the internet bill this month or more naturally this month’s internet bill.

Breakdown:

• tagihan = bill
• internet = internet
• bulan ini = this month

Indonesian often puts time expressions like bulan ini after the noun phrase, so tagihan internet bulan ini literally looks like internet bill this month.

In natural English, we usually say this month’s internet bill.

Yes, exactly. Naik literally means go up, rise, or increase.

In this sentence, it means the bill increased:

• tagihan internet bulan ini naik = the internet bill went up this month

This is very natural Indonesian. You could also see more formal words such as:

• meningkat = increase
• bertambah = become greater / increase

But naik is common, simple, and natural in everyday speech.

Not naturally in this sentence.

Bukan usually negates a noun phrase or identifies something as not X:

• Itu bukan mobil saya. = That is not my car.

But here the speaker is rejecting an entire explanation: it’s not that I’m wasteful. For that, bukannya works much better.

So:

• Bukannya saya boros, melainkan ... = natural
• Bukan saya boros, melainkan ... = awkward or unnatural for this meaning

In this usage, it is written as one word: bukannya.

That’s because it functions as a fixed expression meaning something like:

• it’s not that...
• rather than...
• instead of...

Learners often notice that it seems related to bukan + -nya, and historically that makes sense, but in modern usage you should treat bukannya as a standard form.

It is fairly neutral, maybe slightly careful or written-like because of melainkan.

• saya is neutral/polite
• melainkan sounds a bit more formal or polished than everyday tapi

A more casual version might be:

• Bukannya saya boros, tapi tagihan internet bulan ini naik.

That is very natural in conversation.

Because the contrast is already expressed by the structure bukannya ... melainkan ....

The meaning is roughly:

• Not because I’m wasteful, but because the internet bill went up this month

Indonesian does not need to say karena here. The contrast structure itself already tells you that the second part is the real explanation.

If you added karena, you would be making the sentence more explicit, but it is not necessary.

Yes, very likely.

This kind of sentence often has a defensive or corrective tone. The speaker seems to be responding to an assumption like:

• Why are your expenses higher? Are you being wasteful?

Then the speaker answers:

• Bukannya saya boros, melainkan tagihan internet bulan ini naik.

So it often implies:

• someone blamed the speaker
• the speaker is correcting that idea
• the real reason is the higher bill

Yes, a little, but the original order is natural.

For example, you could say:

• Bukannya saya boros, melainkan bulan ini tagihan internet naik.

This also means It’s not that I’m wasteful; rather, the internet bill went up this month.

Both are fine. The original tagihan internet bulan ini naik is natural because bulan ini neatly modifies tagihan internet as this month’s internet bill.

Some natural English versions are:

• It’s not that I’m wasteful; it’s just that the internet bill went up this month.
• I’m not being wasteful—the internet bill just went up this month.
• It’s not because I spend too much; the internet bill was higher this month.

These all capture the same idea, even if they are not word-for-word translations.