There may well be no such thing but, to assist us in at least trying to find a number for you, please indicate the nature of your call. (There are different numbers for phone faults, broadband problems, etc, etc).
Thanks for the responses. I will try Tilly's first and see how it goes. We are having an intermittent problem with incoming calls. Sometimes the phone cuts off after the first ring and goes straight to 1571 answerphone, even though we have an inbuilt answer machine. We tried BT (Indian call centre job) and they tested the line and said all was fine. Then we assumed it must be our handset so we bought a new one and all seemed to be fine for a few days. Now it's started again! Very annoying!
Since you don't need 1571, get it disabled altogether. Phone 150 or 0800 077 771 to get it removed. (It might take a day or two for the change to take effect). Alternatively go to your account details online and, under 'Calling features' remove the tick next to 1571.