Indian Railway Catering & Tourism Corporation [IRCTC] — Provided Mobile Number is already associated with another IRCTC Account.

Hi, I have been using this number from last 17+ years and have been using same number for all IRCTC bookings. Since covid started we have not been travelling much and have not used any IRCTC service in last 2-3 years.
Now when i am trying to use my account associated with same number it is not allowing me to book tickets after successful login, it is showing message that - "Provided Mobile Number is already associated with another IRCTC Account.". On complaining to [protected]@irctc.co.in, the poor customer support people are just arguing to provide proof of the number ownership. Now i don't have any proof as i this is very old number and now prepaid. First of all how come someone else started using my number without my approval ? Second, i have shared screenshot of mobile provide app which clearly shows number is on my name. Kindly resolve the matter as it is causing inconvenience to me in booking tickets as i don't hold any other number.
I dont understand their logic, if i am the owner of the number and i am able to enter OTP why dont they allow with this validation.