When someone opens a bank account with any of the banks or financial institutes which are operating in India they ask the customer to provide many details like name, address etc. along with those details, they will also ask for the mobile number.
The mobile number which will be registered in the bank i.e. in the bank records in nothing but the registered mobile number.
If you want to know your registered mobile number then try to remember which mobile number you had entered in the account opening form.