Terrible customer service

I ordered a pair of Nike sneakers from superbalist and when they arrived I wore them and they seemed to fit though with time the left one felt tight. Only to check sizes and realise that they had sent me different sizes one is UK 5 and one is size 4.5. I informed them and they admitted it was mistake on their side but the fact that I had worn them would be an issue. Now Noone is giving me proper feedback on what I should do coz all I want is the correct size that I ordered extremely frustrated and fed up