As Number-6 suggests above this would be best dealt with by a specialist solicitor who should find it a straightforward matter - the main problem wou!d be to resolve the issue of having his/her correspondence being thrown straight into the nearest bin.
The onus is on VM to provide evidence of the wayleave agreement which has to be signed by the property owner with real ink on real paper. Then the onus is on them to provide evidence of the granting of planning permission - you may wish to contact the relevant Planning Department yourself to check up on this.
To date VM have responded to you with the usual bluster and if you fail to go away it would be miraculous if they took the decision to brief a solicitor to fight the case at County Court and you would win by default with legal costs and compensation and of course costs for removal of the lousy box.
The decision of how to proceed is of course up to your good self but bear in mind that VM will delay and pontificate and obstruct in the hope you will go away.
Good luck with it