Horrifed at Telkom's after sales service

Good day, I have recently took out a new contract at the Telkom store in Musgrave Centre Durban, The lady explained everything on my contract and it was for R289 per month, I receive my statement via email monthly and realized that I am being over charged for the contract, I went to the Telkom store yesterday and the lady at the entrance told me that I should call 10210 and I couldn't assist at all, so I had to go back home and phone , only to find out its an automated response, and they ask for your cellphone number and they rudely cut the call, then I got an SMS saying I must stat a watssup conversation and or send an SMS, so I sent and SMS cause I don't have watssup on that number, and there was no option for billing, so I am extremely horrified with the after sales service, I am getting really upset, I am one of your loyal clients and I always refer business, this is really disturbing at how you treat client after the contract is taken, pushing them away from the store, I need urgent assistance otherwise I am cancelling all my business with you and telling all my friends about the horrible experience. I need reasons why you'll are over charging me.