Top up contract but being charged above

I upgraded my data contract with autopage to 2 gig top up contract in Oct 2015 . I received a steep bill of R1215 for Nov bill , called autopage they said will respond in 7 days but no calls or feedback . I called their customer care line which is an 0861 number spent 10 min on line they said will lodge a complain as I'm on a top up but I received no further info . I called again. Another 15 min on customer care they tell me charges are correct , I tell the lady I'm on a top up once my data is finished I have to top up no be charged , she says she will lodge a complain again . I asked if they could call me , the response we are not allowed to call a anyone back . This is poor customer service , I asked them to check my contract update date and listen to the voice recording to confirm it is a top up contract but still no joy . I have many cell contracts this is the worst I ever owned . I been with Autopage for 3 years , now it is a night mare .It's amazing people can call u more than 20 times to do an upgrade but can't call u to resolve a customer issue . I'm really frustrated at the bad services & incorrect charges poor customer feedback . It is sad to say this will be my last