Parcel post to Germany

Fireboss47

I'm trying to return a high value heavy parcel item (12kg) back to a firm in Germany for a refund but am having an impossible time trying to find a courier or postal service that will allow me to complete the full customs requirements online, I have all the relevant details from the company, vat details/EORI number etc. but when I try to fill out the couriers form it stops me half saying they cannot process my order with the details provided?
There does not appear to be any DHL/UBS/FED EX etc. shops where I can go to for someone to deal with this for me and the phone helplines are staffed by barely understandable overseas staff.

Does anyone have any experience of how to get through the customs minefield?

 Is it worth using a Customs Broker and if so again does anyone have any advice?
The whole process is driving me absolutely BONKERS!!!