I think you will find that the previous owner, who may well have had a BT line, has cancelled his contract with BT. That will involve BT engineers "throwing a switch" in the exchange. In this area (and I am sure BT do this everywhere) having the line switched back on means that BT engineers need to go to the exchange and switch the connection back on. Their normal waiting time is 3 to 6 weeks to "Install a new line for a new customer" ~ that's what they call it and that's the time they take.
When we moved here, about 150 metres from the local exchange, that's what they did to us because the vendor was moving within the exchange area and had retained her number. BT were happy to welcome us as customers, subject to the waiting period, and even offered to let me have my new number so that I could tell people what it would be when they got round to connecting it.
Despite the fact that Nick was a customer at a previous address he came to Nottingham from outside of their area and in the process transferred the BT line to Mrs Nick. He has bought a flat that had been put on the market following repossession by the previous occupant's mortgage holders. They would have had the line disconnected to avoid ongoing rentals, or perhaps the previous owner had failed to pay the BT bill. Either way as far as BT is concerned it all adds up to a "New Installation" and the waiting period for that is as quoted.
Service is a concept that only customers expect and that few, if any, 'service providers' even attempt to understand. They are however happy to take your money.
