BAD SERVICE FROM I-SMART (CELLPHONE CONTRACT)

I HAVE A CONTRACT WITH I-SMART FOR A APPLE PHONE IN AUGUST THEY CAME PICK THE PHONE UP FOR REPAIR AS THE BATTERY WAS SWOLLEN VERY BAD TILL DATE 18/12/2020 THEY DIDNT PHONE ME OR ANYTHING I MUST CALL THEM THE WHOLE TIME I STOP PHONING OCTOBER 2020 AND THEY STOP DEPIT ORDER END OF SEPTEMBER BUT TODAY 18/12/2020 THEY START DEBIT ORDER AGAIN AND ITS UNFAIR AS THEY STILL HAVE THE PHONE, I ASKED FOR A REFUND ON THE DEBIT OREDR THEY REJECT MY REQUEST THE BANK CANT REFUND AS ITS A ADDO DEBIT ORDER, THEY SAID THEY SEND A SMS FOR DECEMBER DEBIT ORDER AND I DIDNT EVEN RECEIVE IT - IT FEELS LIKE I HAVE TO PAY FOR SOMETHING I DONT HAVE AND ITS UNFAIR