tablet not repaired after 2 times

Took tablet in for repairs in December 2014 and only got it back in February just to find that it was not repaired, still had the same problem. Took it back to mtn in April, got it back in May and still experience the same problem, they refuse to exchange it and now because they are on strike they even refuse to take it for repairs again. This item was bought in July 2104 but we only had about 4mths of use. Mtn get their money every month without fail but we do not get the service we are paying for. Tablet doesn't charge and switch off by itself constanly when in use or not on charge.