Another make?

I have a new humax that keeps freezing, John Lewis replaced it. The new Humax has same problems. I bought a new TV and paid for an aerial specialist, then I found this website!!
Techno at John lewis says it is the larger memory models that seem to have the problems.
I can't believe they still sell them.
Do I change to another make whilst I am still in a good refund situation or mess with all the tips given below?