Poor sevice from MTN

Really disappointed with MTN, I have a Samsung 7'' tablet, and experienced problems with the charging point. Took it in for repairs and they actually fixed the problem. After three months we experienced the same problem and when I took it in for the second time they came up with an excuse that there is liquid damage to the phone. Took the tablet to Samsung Rosebank and the guys at the repair desk said I need to tell MTN that they need to fix it free of charge because it still falls under the two year guarantee period. Took it back to MTN and they took the tablet but now they cannot fix the problem due to liquid damage, they never send pictures proving this. On top of it all I have to now pay a fee of R330 or I will not be able to get the tablet back. There was no communication before this stating that I would be responsible o pay any fees. Went back to Samsung Rosebank and explained this to the same repair guys. they advised me to call their Service centre and they might be able to help with this dilemma. called the service desk and a lady said that they cannot help. She was very firm with this statement. What do I do.....?