BAD AFTER SALES SERVICE

i have been dealing with Homechoice for many years and pay a lot of money each month to them but their after sales service is very bad and its not the first time I am going through this. I recently purchased a microwave and reported a few days after buying it that it was faulty. I was told to take it to the post office to send back, after explaining that I was not able to carry the thing i was informed that it would be collected. It is now almost 3 months and it has still not been collected yet I am being billed for a faulty microwave that I cannot use properly. Their excuses: they have tried to phone me - they have not!!! They came to my house and no one was there - I told them to phone first and I would meet them there. I waste countless telephone calls and just get no assistance. Its really BAD!!! I even told them just to replace it and send me a new one - that can't be done as they have to do tests etc to see if it can be repaired. Surely they should replace as I reported it a week after receiving it. Something needs to be done urgently