Shein Refused Full Refund for Returned Phone and Offered Only Partial Credit

I ordered a mobile phone from Shein.co.uk on 14 May, to be delivered to Southampton, Hampshire. The phone cost £70. When it arrived, it was extremely slow and not working as expected, so after trying it for a very short time, I decided it was not acceptable. I returned the phone on 5 June, packed carefully and bubble wrapped, in the same condition it arrived in. I have now received an email stating that I will only be refunded £7 because the phone is allegedly “used or damaged”. I strongly disagree with this, as I only used the phone briefly to see if it worked properly, and then returned it. It was not damaged when I sent it back, and I made sure it was well protected in the packaging. I feel this situation is unfair and that I am effectively being made to lose a large amount of money through no fault of my own. My order number is GSO1YA34900003GS. In this situation, I request a full refund of the £70 I paid for the phone, as I returned it promptly due to performance issues and did not damage it in any way. I am not in a position to lose this amount of money, and I expect Shein to review the return properly and resolve this issue by refunding the full amount.