Poor service

In January this year I upgraded my internet package to a 10Mbps line. I have had endless trouble with this service since about June / July. For no reason I am logged off the internet whether using the LIT box, laptop, tablet or cellphone. It is incredibly frustrating. When I upgraded I got a new router - apparently the best that Telkom have. I think it's a Zycel. Out of desperation I decided to take the router in to be checked only to be told it was not faulty. They also have refused to have it sent away to be checked because it will just be returned as not faulty. I have in the meantime have got a router from a friend. The difference in unbelievable. They still will not listen to me. No technician has come out to check the line. They just keep closing the fault without it being resolved!!!! What can I do??