Pliers being necessary sounds like bad
threads in the
tank base or the coil threads were bad from day one. I had a Y3S that was that way and fortunately took it back to my local over-priced local store and they couldn't get it out ...... until they used a very SMALL pair of pliers. The new coil wouldn't go in and luck was on my side after 20 minutes of "discussion". They replaced the whole assembly after checking all fit as designed.
It sounds like you have an issue with one or the other. Did a new coil go in OK? If you still need pliers ..... get a mall set until you can replace that
tank BASE........ which I found for my T3S-------->
EGO Kanger T3S Replacement Base [T3s Base] - $1.20 : Vapors Choice, Ecigarettes & Parts Perhaps they have one for yours - I don't know if they are replaceable so this may be of NO help.
Good luck! Perhaps they have one for yours.
Senile Old Man Don