I have a sim only contract with telkom which i pay R200 per month since last year may

I have a sim only contract with telkom which i pay R200 per month since last year may. In November i reversed a debit order due to other reasons and automatically debit order stopped running well thats after i query but i did understand it was my fault. But since November last year i have been paying via eft every month end without any problems until this month when out of the blue the debit order runs and i had already payed like i always do well because i could not afford double pay i reversed the debit but to my surprise telkom did not allocate the R200 i payed and i am now owin double the bill i have sent the proof that i have payed on time like any other month but they refusing to allocate my payment. I have sent several emails but i am not happy with the response.