DEBIT DOUBLE AMOUNT WITHOUT PERMISSION FROM ME

SO CELL C calls me today telling me I missed a payment, which never happened since iv been with them for so many years, I told them il have to check my account and if so il go instore and pay the amount they talking about..so today is debit day AND WHAT DO THEY DO...THEY JUST DEBIT DOUNBLE OUT OF MY ACCOUNT WITHOUT MY PERMISSION AND AFTER I HAD SPOKEN TO THEM AND SAID IL CHECK ..and I just spoke to the cell c lady who told Me it was fine I can make payment instore for this amount she is talking of, after I check...BUT STILL THEY JUST DEBIT THEY DNT CARE WHICH MONEY OR WHOS MONEY THEY TAKING OUT OF MY ACCOUNT WITHOUT PERMISSION AFTER I HAVE JUST BEEN ON THE CALL WITH THEM THEY JUST DO THEIR OWN &@^^#