Paytm — Not receipt cash back

Dear Sir,

I paid my electricity bill and use promo code but I have not received cash back.
I have use promo code successfully than money added in my wallet then I have receipt a OTP and open my massage inbox check for it after that My Paytm App closed. Then I Started paytm app and use promo code but promo code Box Given massage this code can be use one time only.