Renewing fixed interest rate

We had a 2 year fixed rate of 4.09% which expired in April 08, we got letter from bank on 21st May offering us new fixed rate options or variable rate. I rang the bank and they offered a lower rate of 4.85% and sent out the letter offer which we had to sign and return on 26th May. We signed & posted back on 27th. Today our mortgage payment has been taken out of the account at the variable rate which is considerablly higher than the fixed rate. I know we only posted letter back to them yesterday and obviously they would'nt have received it in time for this months mortgage payment. I'm just wondering if they should have sent the offer letter out to us earlier and if i could ask them to refund us the difference perhaps?
thanks

What does the original offer letter say would happen when the fixed rate period ended? If it said it would default to the rate that was applied then they're covered.

Was the 21st May the only correspondence received?

It's your responsibility to track/manage/review your rate - http://www.askaboutmoney.com/showthread.php?t=82452

yea the first letter had fixed rate options - 2 years, 5 years and it said if you don't want to take one of these rates it will default to the variable rate. (i will check the exact wording on the letter this evening but i'm pretty sure the jist of it was if you don't tell us you want a fixed rate we're putting you on the variable rate). the first letter we got was on 21st May, i phoned them, the offered lower rate and got that letter on 26th. i suppose i should have rang them earlier in the month