The Post Office / Royal Mail are almost as useless as NTL. (No Offence to anyone who works for either company).
I remember a few years back when I had to send my exam results to a university that I had applied to. I sent them First Class Recorded, and waited for a few days to be delivered. When I checked on their website, I was informed that there was some sort of problem and to phone the helpline. I did this, and was informed that there was no record of my letter having entered the "recorded" system.
I was then advised to send the letter again but this time by "Special Delivery", which at the time cost £2 more. I begrudgingly did as I was advised and this time the letter was delivered.
This time it did arrive.
What Im trying to say is, dont necessarily think that NTL have your letter in their possession - it may not have even reached them yet - recorded or not.
James