It is a scam where the scammer tries to get into your account. They have obtained your phone number and email address from some where and they use the email address to try and access your account.
They then use the "forgotten password" link which will generate a PIN number to your email address or text to your phone which is what would happen if you had genuinely used the forgotten password link.
Obviously in this case it was not genuine so the scammer follows up the PIN being sent with a phone call and claim to be from BT and to confirm that they are genuine they will inform you that they have just sent you a PIN.
In order to carry on with the call, which will be some spurious reason such as someone using your Internet, they will ask you to confirm the PIN to them so that they know you are the account holder.
If you give them the PIN they now have the keys to the kingdom. They can access your account, your emails and email contacts. They will change your log on password and then go through everything searching for bank details etc. and then try and access your online bank accounts etc.
