England UK

I ordered a lovely cardigan off laredoute Iasked for a size 39 I received a
size 43, I phoned them up saying I would like to return this item it was 4
sizes too big, they said no problem their courier would be by to pick it up,
I also asked whilst I was on the phone for the correct size 39 to be sent
they said they couldn't send the new size until payment was made and that
they would refund the payment for the wrong size back to my card once it was
returned, I thought it was a little strange why they simply didn't come by
pick up the old size and exchange it at the same time at no cost to the
customer anyway I made a second payment, the courier came by a week later
and took the old cardigan, two weeks on I haven't received payment back to
my card, and incidentally I have had the re ordered cardigan delivered and
guess what it is the exact same size 43 that was 4 sizes too large, now
laredoute are saying they haven't received the cardigan and I should send
them proof of postage, I have no proof of postage since the courier came by
from the company picked of the cardigan and left.

What are my options?