Following my email to the CEO, I got a call from a Customer Relationship Manager - basically they've dropped the case but in future reserve the right to request outstanding funds or the goods in case of discrepancies, even though this is not highlighted on their T&C. The T&C say a contract is established when they've despatched the item.
Very unpleasant person, but I was not in a mood to argue.
I wouldn't say I was scared, especially after reading their T&Cs, but it was unnecessary stress.
Thanks @BazzaS & @dx100uk for your help.