Learn Hardcore German: Ich habe den Kundendienst mehrmals angerufen, aber niemand ging ran. - I called customer service several times, but nobody picked up.

Because anrufen is a separable-prefix verb. In main clauses, the finite auxiliary (habe) sits in second position, and the past participle (angerufen) goes to the end, forming a sentence bracket. The participle is built as prefix + ge + stem: an + gerufen → angerufen (note that the base verb is strong: rufen – rief – gerufen).

Why is it den Kundendienst and not der Kundendienst?

Anrufen takes a direct object in the accusative, and Kundendienst is masculine. Masculine accusative singular is den, hence den Kundendienst. Compare: die Hotline (feminine) would be die Hotline in the accusative.

Can I say Ich rief den Kundendienst mehrmals an instead?

Yes. That uses the simple past (Präteritum) of a separable verb: rief … an. In everyday speech, Germans often prefer the present perfect (Perfekt): Ich habe … angerufen. In writing or narratives, Präteritum is common. Both are correct here.

Why is it niemand ging ran and not niemand hat rangegangen?

With gehen, the correct perfect auxiliary is sein, not haben. So the perfect would be niemand ist rangegangen. The sentence uses the simple past (ging ran), which is also fine. All correct options:

… aber niemand ging ran. (Präteritum)
… aber niemand ist rangegangen. (Perfekt) But not: hat rangegangen (wrong).

What exactly is ran here?

Ran is a colloquial form of heran, used as a separable prefix in verbs like rangehen. In phone contexts, rangehen means to pick up/answer the phone. Patterns:

Present: Er geht ran.
Simple past: Er ging ran.
Perfect: Er ist rangegangen.
Subordinate clause: …, weil er ranging. / …, weil er rangegangen ist.

What’s the difference between rangehen, drangehen, abheben, and ans Telefon gehen?

rangehen: very common for answering a call.
drangehen: also widely used in everyday speech with the same meaning in this context.
abheben: literally to lift the receiver; still used figuratively for answering a call.
ans Telefon gehen / den Anruf annehmen: neutral paraphrases.
All can fit; register and regional preferences vary slightly.

Why is there a comma before aber, and does aber change the word order?

Aber is a coordinating conjunction linking two main clauses, so a comma is required. It does not push the verb to the end; the second clause keeps normal main-clause word order (verb in second position): …, aber niemand ging ran.

Where can mehrmals go, and does its placement matter?

Typical and natural placements:

Ich habe den Kundendienst mehrmals angerufen.
Ich habe mehrmals den Kundendienst angerufen. Fronting for emphasis is also fine: Mehrmals habe ich den Kundendienst angerufen.
Avoid placing it after the participle: … angerufen mehrmals sounds unnatural.

Can I say Ich habe beim Kundendienst angerufen instead of using a direct object?

Yes. Bei + Dativ is idiomatic: Ich habe beim Kundendienst angerufen.
Both are fine:

Ich habe den Kundendienst angerufen. (transitive)
Ich habe beim Kundendienst angerufen. (at/with the service) Don’t mix them in one clause.

Why is it ging (singular) after niemand?

Because niemand is grammatically singular. So the verb is third-person singular: niemand ging, niemand ist, etc.

What gender is Kundendienst, and why is it capitalized?

All German nouns are capitalized. Kundendienst is masculine: der Kundendienst (Nom.), den Kundendienst (Akk.), dem Kundendienst (Dat.), des Kundendienstes (Gen.). A common synonym is der Kundenservice (also masculine).

Can I use keiner instead of niemand?

Yes: Keiner ging ran.
Both mean no one. Niemand is slightly more neutral/formal; keiner feels a bit more colloquial. Note that keiner/keine/keines also function as determiners with nouns (e.g., kein Kunde).

Is mixing Perfekt in the first clause and Präteritum in the second clause okay?

Yes. They’re two independent main clauses. In speech, Germans often prefer Perfekt overall but still use Präteritum for a handful of very common verbs like sein, haben, gehen, kommen. Hence Ich habe … angerufen, aber niemand ging ran sounds natural.

How do separable verbs behave in subordinate clauses?

In subordinate clauses with a single finite verb, the prefix reattaches and the verb goes to the end:

…, weil niemand ranging.
With compound tenses, the participle stays before the auxiliary at the end:
…, weil niemand rangegangen ist.
In main clauses, the prefix separates: niemand ging ran.

Why is it angerufen and not angeruft?

Because the base verb rufen is strong: its participle is gerufen, not geruft. Add the separable prefix an in front of the participle: an + gerufen → angerufen.