150 and go through to customer service, there aren't really any other numbers to give out, you can lodge a formal complaint regarding it but its likely they will do nothing about it, you'll then be free to escalate it on to the ombudsmen who will then rule that VM did everything required to build the cabinet and rule in their favour, i mean i know its a **bleep**ty answer and not what you're hoping for but realistically they aren't in the wrong and they aren't going to dig up what could potentially end up being dozens of roads just to move a single cabinet without an extremely good reason
Consult the communications code of practice (download it) and read the part about siting of poles and cabinets, if the build is adjacent to a rear garden fence providing solely by itself access to a secure rear garden , flat roof or private property then it is in a secure by design position. It may be illegal, If the local council have agreed to the build and it is illegal then neither VM or your local authority have acted diligently, both parties can be held accountable. Communications companies sign up to the code of conduct and are accountable, if you are a customer of VM then once you have explained the situation OFCOM will address the issue with you. If it an obstruction then you may have a case to get it removed.
Act quickly as time is a deciding factor check your boundary lines as they might have encroached onto your property, boundaries are defined spuriously by HM land registry.
You will not get any guidance from this site regarding this matter as in my experience the community team is limited
1) With knowledge
2) With any authority than to refer you to the defence team!
Virgin Media will also tell you that if the matter goes to court then they are yet to lose a case for an uplift and re siting of any of their apparatus.