Stupit guarantee

I booked in my phone for internal repair, now they charging me saying i misused sim card port. The stupit Sony was working perfectly for 3 months and the next morning it couldn't read sim card and repair department saying it's my fault. I won't pay them any cent. They can keep their phone as much as i care and i will cancel all my contract and they won't debit any cent from my account from now. They can keep their contract then i will also keep my money. What is GUARANTEE if they can really explain it? Blacklist me if you can, I DO NOT CARE. As long as they not getting any money from me then it's fine.