"They did not drink tea."

Translation: उन्होंने चाय नहीं पी।

[ArvindhMani]

Why can I not say पिया?

[B96lXSTM]

why उन्होंने and not वहने? does वहने even exist at all??

[Aakhil6]

Same reason why the plural in English is feet and not foots!
In the above case, it's a pronoun one!
वह ने never exists and it is always उस ने only.
Similarly for the past tense of वे, it is उन्होंने only and never वे ने.

[blaqvernaq]

Can someone explain why the ने form is used? It it something like a passive voice? The tea was not drunk by them? Why does the pronoun form change.

[ErwinRooij]

ने is for transitive verbs and turns the subject into oblique.

In Hindi, all transitive verbs in the perfect form (simple past, present perfect, and past perfect tenses) require a special construction called the ने construction.

In this construction:

• the postposition ने must come right after the subject
• the subject changes into oblique

(...)

What are transitive and intransitive verbs?

Transitive verbs are verbs which normally have a direct object. Some transitive verbs you know are: खाना (to eat), चलाना (to drive), ख़रीदना (to buy), etc.)

Intransitive verbs, on the other hand, never have a direct object. These include जाना (to go), आना (to come), होना (to be), etc.

Source: https://taj.oasis.unc.edu/Hindi.Less.15/grammar.html

[Rima92670]

"Unhoney chai nahin piya" should also be accepted as correct