Bought phone with 12 month warranty - returned and seller wont give fix, return or refund - what 2do

[chiselpix]

This seller sold me this mobile at the end of march, I started having problems with it by july as the phone itself wouldnt read any of my finger interactions and instead would start doing things as if i had been pressing elsewhere. This is a malfunction with the touch digitizer. Now this seller sold me this phone claiming for it to have a 12 month warranty.
http://www.ebay.co.uk/itm/4G-DOOGEE-Y100-Plus-FHD-5-5-Android-5-1-2GB-16GB-Dual-SIM-Mobile-Smartphon...
link to text stating advert and one years warranty.
Now i messaged the seller on the 13th of july and didnt hear back until the 23rd. past another couple messages before a month later giving me a return address, which was.
Thomas Wang
Attn: RMA160803-2714
7 Trident Way，
Southall UB2 5LF
Uk

Now after some googling only recently I figure this is not them at all, this address is for a company called 4px worldwide express, basically a holding place for chinese goods which anyone can resell as far as i understand and they offer RMA serivces.
I returned my mobile phone via next day royal mail tracked and signed: barcode SF208158813GB. 12th of aug they claimed to have recieved my item. they said leave it for 2-3 days and they will have a result. still nothing so i messaged them and get a reply 22nd aug stating they are now forwarding it to test this will take 2 -3 days. every single message i recieve starts off with "sorry for the delayed response because of system problem". next msg 1st of sept, starts same msg, then states they will give me 50% refund, i dont want a refund i want a fixed device under warranty. 14th sept is the nxt time i get a msg saying 60% refund because i have used the phone for some time. i do not call 3 months much use of the phone before breaking. anyway i was becoming sick to death of the struggle of getting msgs back i said i would accept, however to this date i am getting messages saying to wait till next month for refund. This is not acceptable and now theft in my eyes, i have paid for something, returned in good faith and now cannot get my phone fixed or not fixed or refund.

what can i do? do i have a leg to stand on and why is this seller still allowed to sell these phones with a 12 month bogus warranty if it means naff all and they just keep the phone and offer nothing.