I can't answer your question as to why your friend did this to you. I strongly advise you to write to the company again stating that you are not responsible for this person's debts. State that you have been illegally harassed for money you do not owe (telling you you will have to prove the goods are yours is definitely harassment) and tell them that if they persist in their actions, you will sue them for compensation for the distress they are causing you. Also state that you want to know if they have blacklisted your postcode so that you can record the true facts. That should do the trick.
