right I see the confusion...
It would appear that when I had moved to the VIP package (circa 2yrs ago) I had my V+ installed and standard box moved without paying any installation costs, however they put £10 on my monthly bills for the pleasure.
So when I requested a V+ box (ie a 2nd V+) to replace my standard they wanted an install charge of £50 AND an extra £10 per month....it was this I wasn't happy with.
So, after speaking with retentions, they looked at my history to understand what had occurred etc..... thus being able to charge a reduced retrospective install fee of £75 which enabled them to whipe out not only the additional monthly cost of £10 but also the £10 additional following my initial install...
I hope your able to follow this, 'cos i think I'm struggling myself now....
