RR were great about a return I had. UPS were very poor.
I followed the instructions, including the BREXIT customs forms (triplicate).
After a week I got daily emails from UPS saying, effectively, that the shipment was held up in some UPS depot awaiting documentation.
Eventually I made contact with very helpful Swedish UPS who moved things along a little bit. That is, the emails have a different phrase but essentially the same thing: package stuck, awaiting documents.
Since then I’ve had occasional calls from a poor lady at UPS who apologised profusely for the non-movement but still hasn’t reported progress.
I had thought that DHL were the least effective international package firm. Now I think it is DHL into the U.K. and UPS out. My sample is very small so my experiences may be unrepresentative.
Good luck.