please help, re consumer rights

df03

just wondering if anyone can help regarding my rights.
in early nov 2013 I bought a Tesco hudl from Tesco direct, within a couple of days I noticed that the screen freezes, so phoned and it was exchanged for a new one.I quickly noticed that the new one also did the same and was told by Tesco it is a well known fault and told I could return to store for exchange or refund, but unfortunately I have a disabled partner and my child was very unwell with chicken pox and so didn't get round to taking it. I phoned them a few days ago and was told that because it was over the 28 days I wouldn't be able to get a refund unless the store wanted to give me a refund, so I agreed to let them send me yet another replacement, didn't want another because I have found them to be rubbish because of the fault but due to circumstances didn't return in the 28 days so had to agree to it.
The replacement arrived today, a dirty disgusting stained model, which again had the exact same fault, I telephone them yet again and was told that they are grade A reconditioned, but they will exchange it because of the state of it, BUT if it wasn't for the stains they wouldnt exchange it because of the fault and the previous customer service fella shouldn't have exchanged it for me because it is a well known fault and they are just waiting for an update, they don't know when an update will be ready though
I am really annoyed, I bought and paid for a brand new item, it was faulty and now I am being fobbed off with a second hand item that they know will also be faulty but they will at some point over the next year sort out an update.
Im not at all happy, Can anyone help?

df03

can anyone help?