Tablet went in for repairs for more than 3 months

My Samsung tablet was booked in for repairs on 31/03/2015 and it is still not repaired, no feedback from Telkom Mobile and I'm paying for the device every month. The first excuse was that the device was out of warranty whereas it booked while it was still within warranty period at the time that it was booked in. A proof of purchase was sent to repair centre to confirm the warranty but still the tablet was not repaired. When I call the customer service I cannot get any help and nobody knows whether the tablet will be repaired or not and Telkom Mobile expect payment at the end of every month. Can someone please assist, the serial number of the tablet is ***.