Have you ever lost you phone number because it has not been in use?
I’m sure many of us have.
Is this number still linked to your banking profile or / and OTP or as a secondary OTP backup number?
The new person with your number will get access to your account and be able to do any transaction they please.
The cellphone companies do not care and never really warn you about this.
Is your number linked to your Google Account for backup verification? Your FaceBook and Google accounts can get hacked to this way as well.
HOW TO FIX THIS: Please make sure that all your bank accounts and other internet accounts are all up to date and that your old numbers are either working or not used anymore even as secondary contacts on accounts.