Mtn
Account Paid, but my line closed

I have two MTN contracts, I paid R600 last month at their Watermall Fall in Rustenburg. Today, I am told that ammount does not reflect. And they closed the other line, now they want me to fax the receipt. Why the should I fax that because I stood in the que for an hour and half to pay R600. Why is it my problem to prove that I paid? I was about to upgrade, now I am not anymore, you take your customers for granted MTN.