09-06-2018 9:14 PM
Unfortunately you did this all wrong, it makes it much harder to explain what to do now.
What you should have done was to return it under eBay's money back guarantee. You would have received a full refund and the seller would even have had to send you a prepaid return label.
You haven't told us when you received this phone but if you're within eBay's time limit you may still be able to open a case through through the resolution centre: http://resolutioncentre.ebay.co.uk/
A case must be opened within 30 days after the actual (or latest estimated) delivery date. When required, you will need to enter the tracking number or delivery number (from your proof of posting) to prove that it was returned to the seller. After 8 days the option will appear to escalate the case for eBay to step in. If still unresolved escalate it, and don't agree to close the case before you have your refund.
If it's already beyond eBay's 30 day time limit you can still open a case under Paypal's longer, 180 day buyer protection policy. Be sure to escalate the case within 20 days. PayPal will also require proof of delivery. Make it clear that the phone was faulty on arrival.
Failing that, as this was a UK business seller you have a statutory right to return it for a full refund.