terrible customer service

I had a Pandora bracelet for Xmas from the Cardiff store. It has always been big and I was told that with more charms it will become tighter. I have worn it a couple of times and it is practically falling off. I no longer hold the receipt. I took it back to Cardiff and they measured the bracelet which was 19cm however my wrist size is 17cm. The assistant said they could make bracelet shorter at a cost of £20. I do not see why I should pay this as it is obviously an error with the assistant who measured me and gave me wrong size. I was then told to email Pandora which I have done, however the reply was to go back in store! Would not recommend at all, looks like I am now left with a bracelet which I cannot wear.