I had to call my ISP and the robot at the start requested my contact number (the one they already have listed for me), followed by the # key.
So I typed that in on the mobile keyboard. Then typed in further numbers as requested, to choose the call subject etc.
As it happened, the lines were all busy so they asked if I wanted a call-back, which I chose with another number.
But I then had to enter a phone number again. I began typing it but the robot said sorry, that’s not a valid number, and I noticed my phone was just adding the number to all the numbers I’d already typed.
How do I get rid of the numbers already typed, or start a new one?