Connecting to Remote Win Server 2008 via Virgin Wireless Routes

I need someone in UK who has experience of connecting to Remote Server in this case Win 2008 R2 supplied by Rackspace from users who have Virgin Media Routers.
Connection is via mapped drive. I have users successfully connecting but the ones that cannot all have Virgin Router as the common denominator.

I now have an additional user that cannot Map their Drive and guess what? They are also on a Virgin Router.

I need someone who definitively knows the answer to this problem or can definitively say that it is impossible. I will be honest and upfront and say I cannot afford to throw money at this. I have already wasted 3 days and £50 on this and if it can't be solved today all the users will have to go over to 3G Dongles.
If you are the person I need you will solve this ion less than 5 mins and charge me a token amount. You either know what the problem is or you do not. Experts have spent 1 and half hours in one of the users PC's and Router without success.