Airtel — decline of porting the number to another service provider

I am writing with sheer disappointment and the inability of officers from airtel to provide a satisfactory response or evidence to my complaint.

To cut a long story short, i had requested one of my mobile numbers to be ported out to another operator. The request was declined on the premise that the number is not 90 days old. However this is incorrect.
The number was changed from prepaid to postpaid but has always been with airtel on postpaid before being made prepaid for a brief period of time. Thus by all means the number has been with airtel for many many years and has never been ported out ever.

All i want is a confirmation that this understanding is correct or not. If this is the case can i be provided with evidence of such a rule please?

By declining my port request airtel seems to be devising their own rules and refusing to approve the porting request.

They have also not provided a complaint number to the various emails that i have sent raising this issue.