CONTRACT ISSSUES

I HAVE AN ACCOUNT WITH CELL C, WE HAD A DEBIT ORDER AGREEMENT THAT THEY WILL DEDUCT R150 EVERY MONTH, BUT AFTER A FEW MONTHS I WENT THERE AND CANCELLED THE DEBIT ORDER BECAUSE OF FINANCIAL CONSTRAINTS, THEN WE AGREED THAT I WILL PAY AT NEDBANK ON THE 30TH OF EACHMONTH, BUT NOW THEY STILL CONTINUE DEDUCTING THAT AMOUNT FROM MY ACCOUNT AND I DO NOT HAVE MONEY THERE SO IT BOUNCES BACK AND IM LEFT WITH AN UNNECCESSARY BANK CHARGE. EVEN NOW I HAVE A NEGETIVE BALANCE OF R-533. AND ALSO CELL C CANCELS MY NETWORK ON THE 20TH OF EACH MONTH BECAUSE I HAVENT PAYED BUT WE AGREED THAT I WILL PAY ON THE 30TH OF EACH MONTH