I have a similar problem at an earlier stage. i expressly asked BT before signing up to full fibre that they will be able to get my number from Vonage. No problem i was told. 4 attempts to port have failed. I had to initiate the request 3 of the times. its logged as a complaint now yet noone from BT has called me back.
My number is originally BT and I also still have my copper line. Having to pay two broadband and line bills is frustrating but nothing compared to the worry of losing my number. (EDIT apparently I'm not paying BT until number migrated, my mistake. And just to add although unresolved the BT engineers I have spoken with are very helpful).
I imagine Vonage is in India and in the peak of its pandemic ?