Charged for a service that I am not receiving

I made contact with MWEB, to change my fibre internet service provider from the 1st of September 2017, I also elected to upgrade from my current 10Meg fibre line, to a 20Meg fibre line, and I was assured by the MWEB sales consultant that all was done & ready to go. When I test my fibre line speeds, this is no more than 10Meg, and many times only shows 5Meg speed. I have contacted MWEB a number of times, but am told that Telkom have not upgraded my line to 20Meg speed (This is Mweb's responsibility, not mine). MWEB are charging me for an uncapped 20Meg fibre product, but I am only getting a maximum of 10Meg. I am being charged for a service that I am not receiving, and despite numerous calls, e-mails & complaints lodged with MWEB, I'm yet to receive a resolution, and they will not provide me with a senior manager to escalate the problem to. MWEB owes me a refund for the difference between a 20Meg service & a 10Meg service for the last 3 months that I have paid for, and if this issue is not resolved I will cancel the service with MWEB with immediate effect, as well as lodge formal complaint to the DTI, National Consumer Commission, and Consumer Watch.