Pathetic service on billing error

In June of this year, I asked to load a 20gig once off data bundle on my Glocell account, this cost R999, so it's quite costly. The guys at Glocell "accidentally" loaded it twice and charged me for it twice. Since discovering this, I have logged a call on their website as well as phoned them probably 10 times to get this corrected. I have logged this complaint with them every month after receiving my bill since, but today I received my new bill and STILL it hasn't been fixed. They should have added the R999 credit back at the end of June already, as per my very first discussion with a agent over the phone. II have phoned every month and they ensured me every time it would be done by the next bill. Still nothing. This is Pathetic, I don't think they will EVER get this right.