This fault is known as a Ring Trip and is quite a common occurrence. It is caused by a part of the wiring putting a partial short on the line making the telephone exchange believe someone has picked up the telephone when the number is called. A majority of these faults tend to be located within the customer’s property, so can often lead to a hefty bill if a BT/Openreach engineer visits. Common causes of this issue are damp sockets, faulty filters or telephone equipment, and damage to internal or external cabling. Contact me for a visit, where I can locate and resolve the issue at a much cheaper price than Openreach.