RETURN NOT COLLECTED

I bought sneakers. Then received my parcel but then sneakers were big. I logged a return it was approved. The courier never collected the parcel and no one called me. I sent emails with no response till I called customer care then I was told my period has expired and the courier claimed to have called me twice with no answer. I requested proof that I was called because I have missed any call from any number and if I did I would have called back. Now the parcel is with me and they are refusing to collect it. If they can provide me with proof that they called and I didnt answer twice then I will take the blame.