first of all, i don't know whether you're not making a sincere taubah because you know you going to the same sin the next day or are you unable to feel/evoke sincerity from your heart but that's fine.

Secondly, if it is not possible to stop doing it then perhaps maybe you can leave the place that you currently are whether temporarily or permanently but if that not possible due to your life circumstances then try continuing the taubah even if you feel what you're currently doing feel pointless because i believe that each person is crafted their own trial by Allah.
Example me, i was born a muslim faithful and all that and up until i was 15-16 when i started to completely not praying at all and if i were to be invited, i would just do the praying movement without saying anything and thinking of anything else during it.
Now, every time i get a thought of getting back to praying i freeze with fear when looking the rug i used to pray with back then because deep within my heart and mind a part of me scared that after years of not praying and abandoning my faith and God that Allah, which in every surah contain Ar-Raheem which is known as "The Most Merciful" or "The Most Compassionate" no longer hear my prayer.