Billing

I really do not no what to do anymore I've sent emails, and I've tried to call and no one can help me, I had to pay one of my accounts through eft this month and Cell C sends me and email saying they have received my payment and will allocate it to my number, but this month's bill has arrived and they did not deduct the payment I made so the bill is over the amount that I must pay, I contacted them again today and they still cannot help me, so the end of the month is coming close what's going to happen when they take of to much money, because I no they do not reimburse