Unauthorised deduction

Ever since I started using MTN home WiFi I’ve never had peace, is one thing after another…they don’t care about their customers as long they get money. I signed up for a home WiFi with them, I suppose to pay R500 monthly but now after I received the router and guess what it was not working..there was no internet, I tried to reach out to them a countless times but they couldn’t help so I didn’t receive any service from the home WiFi so I decided to cancel the contract and take back the router to the mtn store but now they deducted R1090 in my bank account for a service I didn’t even receive….this is so unfair of them to take my last money for a service they failed to provide