Non-existent admin and harassment.

So back in 2018 I requested cancellation of my account around 6-10 times and nothing was done about it. I get contacted in January this year regarding payment, so I informed the Mix Telematics call agent about me trying to cancel for half a year and nothing was done about it. She then proceeds to say nothing was received with regards to the cancellation. I go ahead and call the cancellation depart AGAIN, after about 1 hour of waiting i finally got through to a person and once again explained the matter at hand. I was put through to another person who was surprisingly helpful he confirmed a settlement amount that is needed and that a form would need to be signed and emailed back. So a received a document stating the exact settlement fee which I paid with the reference required as well as sent the signed cancellation form back. A week later I haven't heard anything back and ofcourse thought it was finally sorted, but I was wrong. I get a call from lady asking me to pay X amount for my account. I told her I went through the cancellation process and paid a settlement fee a week ago, she acknowledged this and ended the call. That was in January. Now every week I've been getting the same call demanding X amount and proceed to explain the situation again and again. Clearly Mix Telematics can't get their admin in order or run a business. This degrading harassment is getting too much and needs to sorted out ASAP before I pursue legal action. What I will give them is the fact they are reasonably priced, some would say cheap, but I guess you get what you pay for.