(2-part post):
It's probably too late for a refund.
Your right to a refund, in respect of defective goods or services, only lasts until the point when you've legally 'accepted' them. This period isn't fixed. If say, you bought something like a stereo system, the pre-acceptance period might only last for a day or two. (i.e. just long enough for you to get the system home and check that everything is working). For other items, the pre-acceptance period can be much longer. For example, you might buy a car in November and not discover until spring that the air-conditioning doesn't work. It could then be argued that you'd not yet accepted the car because you hadn't had time to check that everything was working. (That's not just a theoretical example; it's actually been tested before the courts).
If you've been in continuous dispute with MFI since you bought the kitchen, then it's clear that you've never legally accepted the kitchen, and your right to a refund remains in place. However, if you reached a point where MFI seemed to have put everything right (so your thought that your problems were over) or where you said to them 'OK, I suppose it'll have to do', then you've accepted the kitchen and you no longer have a right to a refund (even if all of the doors fell off and the drawers completely disintegrated just a week later).