The "90 day rule" is just a policy that telcos framed to lock out a customer. That can be broken if you can communicate to a higher authority and explain the case. I once opted to port-in to Reliance GSM. The store representative without my consent gave me a postpaid connection, which I realised after the number got ported. I somehow contacted a higher rep and it was converted to prepaid within 3 days after the number got ported. It only took 2 hours after I got in touch with the representative. If the mistake is on their part, it is possible to get things fixed.