So disappointed in MTN South Africa

I took out an uncapped home internet with MTN in May. It worked very well until I moved and changed my address. I took it back two weeks ago. They said there is no coverage at my new address. They offered me another device which provides data that is less than the previous one. I had to cancel and return their router and it was working as they first tried it on their side. Today I received an email saying that the router is not working and I have to pay a fee.