GOT AN CONTRACT BUT NOT HE ONE I AGREED TO

HI I HAVE A PHONE CONTRACT WITH MTN. THEY PHONED ME AND TOLD ME I CAN UPGRADE BUT I WANTED TO PORT FROM MTN TO VODACOM BECAUSE WE DO NOT HAVE A MTN BRANCH IN OUR TOWN. BUT I THOUGHT LET ME HEAR THEM OUT. THEY TOLD ME THEY PHONING FROM SUMMER TRADING AND THEY DO CONTRACTS WITH MTN SO I THOUGHT NO GOING TO LEAVE IT BECAUSE I ALREADY HAD A PROBLEM WITH IDENTITY THEFT SO I TOLD THEM NO I WILL GO TO THE BRANCH MYSELF AND THEY CONFIRMED TO ME THEY ARE WORKING WITH MTN SO WE WENT ON. SO THEY TOLD THEY HAVE A SPECIAL. WHERE YOU A GET THE PHONE, 1 GIG OF DATA,250MIN AND I THINK 20SMS A MONTH FOR ONLY R285. MY PREVIOUS CONTRACT WAS R388 A MONTH.I TOOK THE CONTRACT BECAUSE IT WAS A GOOD DEAL. BUT THE PROBLEM I HAVE IS MY MONTHLY DEBIT ORDER NOW IS R411. I GOT VOICE RECORDING WHERE I ASK THE LADY TWICE IS R285 AND SHE SAID YES. SUMMER TRADING HELP ME TO A POINT BUT THEY JUST SAY I MUST SPEAK TO MTN AND MTN SAYS I HAVE TO SPEAK TO SUMMER TRADING. NOW I SIT WITH ALMOST R126 EXTRA A MONTH I HAVE TO PAY. IF I HAD THE MONEY NO PROBLEM BUT I TOOK THE CONTRACT BECAUSE ITS HELP TO SAVE AGAIN ON SOMETHING ELSE. WHAT CAN I DO?