Pathetic service!

I upgraded my mobile contract in September. I was given 10G 'free' data for 3 months (sept to dec). However my bill for September reflected an amount to pay of R800. Upon enquiring, I was told that I was roaming on the MTN network. I was never told to look out for the MTN sign on my phone when using this 'free' data. I've been trying to get Telkom to sort this out but have been unsuccessful. Spoke to Nontobeko, who gave me her team leader's details. This team leader, Nokuthula Ngozo never bothered to call or email. This is not the first time I've had problems with Telkom. Their service is pathetic and appalling!!!!!