Unfair and greedy behaviour from Vodacom

Vodacom is a really unfair network provider to deal with. I am a prepaid customer for over 20 years and recently took a sim only contract with them at R299 a month for data. I was ****** for my phone in April this year and called them asking them to cancel my account. Now i pull my credit report expecting to have a balance of R299 (1 month arrears) however its now R1800!!!! They have been billing me every month even though the sim has been suspended. Why charge me the full amount of R299 for all these months from April when you have stopped my data from April?????? Pathetic group of people and you will be overtaken in time and i will be the start. MTN here i come