Demanding letter for something not received!!!!

In December I went for an eye test in order to do new specs. After a few days they called to say the specs are ready for collection, once I got there it was found that they were not right and had to be send back. After a week or so I had to call the place to do a follow up, on my return it was found that they were still not right. I waited so long and refused to take the specs and left them at the office. After more than 6 months I received a call from PRS and Associates, wanting to forward me a letter of demand. Immediately I went to the shop to find out what the story is, once the owner directed me to his office trying to find out what's happening. I told him that they messing up a person's name and I'm not going to leave things like that, he started screaming at me and pointing his finger directly in my face. Not once did I receive any email, sms or call from them and after so many months they handed me over for something I never received!! They have no idea what client service is about and how to treat their clients and then they expect me to pay for something I NEVER received and messing up your credit bureau!!