Billing Havoc (PLZ HELP)

In November 2017 I ordered the HOMEunlimited 20Mbps Uncapped month-to-month deal (excluding modem) for R999 p/m online. Sales contacted me to confirm my order for R999 p/m (Nothing more as the deal included line rental). End of November my line and internet was activated. When I received my first bill I saw that they put me on another deal (Home uncapped 20Mps) which they billed me +- R1700. For the past 6 months I have been trying to get this resolved on a weekly basis by this person then that person who are all clueless of what to do. I continued to pay only my R1000 p/m as agreed and my account is now so far in arrears that they have disconnected my service multiple times which after a fight was connected again. PLEASE HELP to rectify my account as per agreement?