The correct pronunciation is [fɛt].

You can listen this in "Prononciation" section of Wiktionary.

The mainstream pronunciation is /fɛt/,
with a southern French accent, that might be /fɛ:tə/,
with some eastern French accents and Belgian ones, that might be /fɛ:t/ or /fe:t/,
and finally in Quebec, the ê normally becomes a diphthong or a long vowel so you might hear [faɪ̯t], [faɛ̯t], or [fɛ:t], the latter mostly in official settings. On the other hand, [fɛt] (with a short vowel) will always be interpreted a representing fait or faite, the p.p. of faire.

In any case, nobody pronounces it “sete“.

I pronounce it the same as “faite”, if you want it without the IPA. My accent would be closest to Parisian. The “ê” is usually pronounced ɛ, like an e before double consonants for instance in chienne.
Bonus: The origin of the circonflexe or “hat” accent in this case was the replacement of the s in the old french version “feste”. It’s still there in other forms of the word. For example, “des activités festives”. Frequently the accent denotes this deletion of another letter/sound, but this is not always the case.

It is consistently pronounced as “FET”. Perhaps you had confused it with somebody saying one of the following: cet(s), cette(s), or c’est?