Side button double click app purchase suddenly stopped working and not restarting again

Just 10 days back I purchased a new iPhone-12.. All was working fine.. suddenly one day the double click side for purchase button feature automatically got disabled and such downloads started asking me to activate assistive touch.. Since then..,

1) I have tried multiple options to reenable the double click purchase option

2) It works only if I enable the Switch Control, which was not the case earlier.. neither do I need Switch control to enable since it acts funny and not needed by me..

3) I also tried the side button option menu option and activated side button payment.. but as soon it is done the assistive touch starts automatically alongwith and the problem remains as is..

4) Since I am in India, the wallet menu option does not show neither Apple Pay nor the side button purchase activation option

5) It was working earlier.. it worked for 5-6 days and then suddenly stopped working and would not reactivate

Need guidance to resolve this from some senior technician..