Poorvika Mobiles — complaint about cash back

Hello.
  at time of purchase they said i will get 775rs cashback within 90 days. After three month it was lockdown. I went 3 times to the shop after lockdown but no proper response from staff. So today 6.9.2020 i went to the shop to ask my cashback but they are asking my bank statement hardcopy from the date i purchased till the date now. But i showed them from my mobile. I don't want to give my card statement because it will have my personal details like credit limits etc. I spoke to customer care officer sameer 3 times but no proper clarification from him too. I am upset with the service