The worst service provider I have ever seen

This issue has been dragging since January when I realised I have been over charged on one of my lines. .Apparently the promo service fee was changed. .I was initially paying R478. .but I got a ridiculous bill in December and January. They acknowledged the mistake and said that will be rectified. .They have changed it to R528 and difference of R50 from what it is supposed to be. .meaning it's still incorrect by R150.. R50 a month since the incorrect billing started...Now I call the call centre to query that and a person puts me on hold for 30 mins and still not come back. .This is unacceptable. .I'm moving to prepaid in June and then port to another network. This is just unacceptable. ..you guys don't care about your customers. .I'm tired of always being on the phone over the same issue. .I want the billing corrected back to R478 and the account being credited accordingly. .