Product paid for is not what I received

I took out a contract with Telkom for wifi and a router in 2016, in 2018 when the contract was expiring, received a call from a salesman with an offer to double the monthly data and receive a new router. My old router is in perfect condition but we agreed on the new contract for double the data at a slightly higher rate than the previous contract. It is one year into the new contract and still yet to receive the double data that was sold to me. I have called and visited Telkom stores to no avail. I have lodged queries which were "resolved" stating that I am receiving the correct amount of data as per the sale, yet my bill, their system and their itemized billing all prove that I still receive the old amount of data, not the double up. The process to resolve this has been appalling. I have been waiting since 5th Aug to receive feedback on yet another query on this, and was told in store today that Telkom can't really help because an external company sells these products on behalf of Telkom. Why does Telkom send the invoice if they have no control over the account!? I was not able to cancel my contract in store and was told to go online to do so, which further frustrates the situation. They were unable to tell me who the company was who sold this product because they don't keep this record on their system (which makes no sense) and have no real process to try to resolve an issue in a timely manner, it is handled via a query which can take weeks for someone to investigate and respond to. I have wasted money on a product that I don't benefit from and wasted time on a problem which really isn't that difficult to fix. Thoroughly disappointed