eh. WTH is this.

tell them off -

was there ANY AGREEMENT on the no 10% refund?

tell them also that it was THEIR MISTAKE and telling you WRONG PROCESSOR and now they got the cheek to keep the 10% for their mistake?

talk to their manager. if they won't budge, i think you should report to consumer and various authorities.

if you return the goods for no reason whatsoever, that i understand. but if it was THEIR mistake - then the 10% is ridiculous.

and next time, PLEASE photocopy your documents before handing back to people.

it's still usable, just the issue here is you are being undercut.