[Android Central Question]

Hello.
I have a network locked S6 that I used it for 2 years by being unlocked with root at a gsm service.
One day I installed a Spotify apk virus not knowing where to look for the real deal and it reset the IMEI to 35000000000006, making the phone stop recognizing any SIM, yet the apk worked as expected providing full non stop play.

I was in the middle of the pandemic with nowhere to go with the phone so I researched and learned how to re-rewrite the original IMEI with z3x, which I successfully managed to do, the phone now seeing when a SIM is inserted. I also installed the latest firmware that was available for this model from this network provider - June 2018, before was April 2018. Trouble is that the initial unlock method have gone and the phone is again network locked.

I have tried to unlock it with z3x with no success, different steps with custom-rom etc so I decided to order the codes online.
I received 2 codes, the unlocking code and PUK code, both valid. Upon reboot if I insert any of them it says that the code is invalid after which at a second attempt it says network unlock successful. The same behavior happens if I try only with the main code or PUK code, but the problem is that the phone remains network locked even after restart, requesting the code again.

I have tried #7465625*638*# and then enter the codes in different order multiple times as advised by the seller yet the same, network unlock successful except that phone is still locked. The phone is in stock mode after a factory reset and I'm out of options google being unhelpful on the matter.

Question is, did I did anything wrong with z3x, damaging something? If so, what and how to repair? Is there any other option to make the phone fit for purpose again, to be used as a phone?