Hmm.
You're entitled to interest, my friend.
Did you make a not of the time and date of the call and who you spoke to? Most calls are recorded, so this info can place the call.
I'd then be writing them a letter confirming the conversation.
Express disappointment that they are not refunding interest (at 8% which is the statutory amount, this could be quite a bit if your �1300 goes back the full 6 years ((5 in Scotland)) - deliver it via the branch, get it stamped and signed by someone there and get them to give you a copy.
Once you have your copy, fax it to the person you spoke to on the phone and keep the header sheet off the fax.
Morale: If someone rings you or offers you something, don't wait for them to contact you. Get in there first and confirm the conversation back to them in black and white.