Vodacom's Poorest service

The reason I'm rating Vodacom with a single star(which I will be happy to rate zero) is because of poor service, I insured my device at a Vodacom store after taking a contract with them, understand this: when I insured the device I took it to the store because I wanted them to see that it's new, what model it is and for them to get the correct IMEI number. I one day decided to check how the cover was doing so I checked online, to my surprise the device covered was now a Samsung galaxy j1 mini but I'm using a J5 and this other device has it's IMEI number which clearly indicates that someone manipulated my account, Quick question: How does any one change details of my cover without my authorisation?, but I was now paying for something I don't own.

I called Vodacom last year (2018) to fix this but they failed and I advised them that I won't be paying the account until this is fixed but even today the problem is not fixed and it is now affecting my credit record because I haven't been paying them.

Seeing that this was hurting me than it is them I again called them this year but because I am angry and disappointed with their service I demanded a refund and i I made it clear that this is affecting my credit record and score so they should refund me and I will settle the account, they have been sending from department to department and no one is helping.

Who can I take this guys to because they are really costing me? I can't believe this is how Vodacom treats it contract customers.