Struggling to get a refund

I am having such a poor experience trying to return items to a retailer that was purchased through PayJustNow. The retailer is unable to process the return because it gives an error saying that the order can’t be located. The Merchant has emailed them and phoned several times and it seems that they are not receiving assistance from PayJustNow to rectify the problem and now I’m being inconvenienced because I can’t return the items that do not fit. It’s the first time that I have had to return something that was purchased through this platform and it is such a hassle. If this is the customer service that they provide or rather the lack of customer service, then I will rather take my business elsewhere. I have never had an issue returning items purchased through Payflex so they seem to be more reliable and offer a better customer experience.