Did you send something like this?
your address
their address
date
Dear Sir/Madam
ACCOUNT NUMBER: **********
Under s77(1) and s78(1) of the Consumer Credit Act 1974, you are ordered to supply me with the following documents:
1) A true copy of the executed agreement relating to the above referenced account.
2) A true copy of the deed of assignment of the above referenced agreement.
I enclose a £1 postal order Serial Number

xxxxxxxx as payment of the maximum statutory fee.
Yours faithfully,
your name
Did you enclose a £1 postal order?
Did you send it by Recorded Delivery?
If so, forget about it. Its their problem if they dont supply this info!