I bought a seatbelt from a vehicle breakers on eBay, the part was faulty and the seller gave me a postage label for return.

no shops accept the courier that the seller uses. I called the courier and arranged collection.

the courier is saying they attempted to collect the item twice, but they didn’t and I also checked the cctv to see if I had missed someone.

the seller isn’t being helpful at all.

do I just post the item back myself tracked? Or continue to attempt to arrange collection from this questionable courier? 
the item is supposed to be returned by tomorrow, I’m not sure what happens when that timeframe expires?

any advice much appreciated