VM has 30 days, from your service being activated, to credit your account with any compo due.
VM routinely tries to dodge or reduce compensation payouts, as reported in topics on here.
If the compensation is not paid, you can (should) escalate to the ombudsman via the processes and timescales here
https://www.commsombudsman.org/our-process
A crackling line on a phone connection via the hub is unusual. Past topics have mentioned issues with the VM phone adapter (poor quality adapter or poor seating in the socket) as well as issues with connecting leads to the phone. Other interference problems have been mentioned when using cordless phones if the phone base is too near to other electronic equipment.
Is your phone connected direct into the back of the VM hub or has VM wired in your old telephone wall sockets so that they work via the VM hub?
You should get a reply from the VM forum team here, usually within a few days, who should help with the above.