Continued Bad Service

I have just been to CNA Centurion, and I received such bad attitude from the security guard to the ladies at the till including the manager. I am currently collecting the Marvel comic books range, about 2 weeks ago I purchased books 17/18/19, my son realized last night that I had bought 2 of book 17, I went to CNA and asked them if it is possible if I could exchange it for book 20. The book is still in its original packaging. Well I was told they will not help me without the slip as to many people are committing *****. I told the lady I am honest to say I don't have the slip and book is in its packaging, to be told there is no proof that I purchased it there so they will not help me and the book 17 is no longer on their shelves, which is amazing as when I collected book 20 book 17 was on the shelve. This is the service that Centurion CNA has been giving for months, they are always rude and stand around talking at the tills when the people are waiting to pay. I want this book exchanged with an apology.