HANDBAG RETURN

I have bought a bag from Charles and Keith in Canal walk about 5 months ago. I recently noticed that this bag was tearing on the handles, which is unusual for a bag with that brand name and with the amount of money spent to buy a supposedly good quality bag.I contacted Charles and Keith to organize a return and replacement of the bag, and their response was that they do not have stock of this exact bag anywhere anymore, and instead I can return the bag to the store for a refund.I explained that I do not want a refund, I would then want to exchange it for a new bag. An arrangement was made by TFG for me to go to the Charles and Keith Store to replace the bag, however, I did not have the proof of purchase on me at the time. I was told by the store manager to only come back when I have proof of purchase, then only will they be able to help me.<br> I asked if they could not check on the system under my details to see that I did purchase the bag in this store, and they simply said they couldn't. I had to return home, and when I found that I have misplaced the proof of purchase. Now I don't know what to do, as they have been unable to help me with this situation. This is very Unproffessional