De levererar paketet till fel adress, så jag måste ringa.

Yes, levererar is present tense of leverera (to deliver).
Many Swedish verbs form the present tense with -ar (common for -a verbs):

• leverera → levererar (present)
• levererade (past)
• levererat (supine, used with har)

paketet is the definite form: the package. Swedish often attaches the definite article to the noun as an ending:

• ett paket = a package
• paketet = the package

Here it’s a specific package the speaker is talking about, so paketet makes sense.

till commonly means to (movement/direction toward a destination). For delivery, till is the natural choice:

• leverera något till någon/någonstans = deliver something to someone/somewhere

Other prepositions would change the meaning. For example, på is more like on/at and is used in some location contexts, but with deliver, till is the standard.

fel here functions like an adjective meaning wrong/incorrect, and Swedish often omits the article in expressions like this when speaking generally:

• till fel adress = to the wrong address

You can also say:

• till en fel adress (less natural; sounds like to an incorrect address in a more “one of several” sense)
• till fel adress is the idiomatic everyday phrasing.

fel is an irregular adjective: it does not take the usual -t in neuter and doesn’t inflect like many other adjectives. It often stays fel:

• en fel adress
• ett fel nummer
• fel sak

So fel is correct as-is.

Both exist, but they mean different things:

• adress (indefinite) = an address / address (in general)
• adressen (definite) = the address

In till fel adress, the structure is like an idiom meaning to the wrong address, so the indefinite form adress is normal.

The comma separates two independent clauses: 1) De levererar paketet till fel adress
2) så jag måste ringa

så here means so/therefore, linking cause and result. The comma is standard and makes it easier to read.

After modal verbs like måste (must/has to), Swedish uses the bare infinitive (no att):

• jag måste ringa = I have to call
• jag kan ringa = I can call
• jag vill ringa = I want to call

att is used with many non-modal constructions, but not after modals.

ringa means to call (by phone). You can leave it implied, as in the sentence, or specify:

• jag måste ringa = I have to call (someone / them)
• jag måste ringa dem = I have to call them
• jag måste ringa företaget = I have to call the company

Both can be correct, but they are different structures.

1) ..., så jag måste ringa.
This treats the part after så like a regular main clause with normal order (subject before verb).

2) ..., så måste jag ringa.
This is also common and often feels a bit more “Swedish” because så can behave like a linking adverb that triggers inversion (verb before subject), similar to when a sentence starts with an adverbial.

In practice, you’ll see both; så måste jag ringa is very frequent in everyday Swedish.

No. Swedish verbs do not change for person or number in modern Swedish. The same present form is used with jag/du/han/de:

• jag levererar
• du levererar
• de levererar

So De levererar is correct without any special plural ending.