The distance to the cabinet, regardless of where it is installed, is what counts with VDSL. As the OP is 3 miles from the exchange, if a cabinet was installed inside or outside it he is still 3 miles away which is too far for VDSL.
that's great advice James-C. i'll do that now, and aside from cross my fingers and hope for the best, I think we may have exhausted this one.
John it is not a big Huawei 288 cabinet sitting inside the exchange LOL it's only a small one it can fit into a medium size server rack with cooling fans and interference is negligible compaired to the standard crosstalk we see on most FTTC lines.
also OFCOM do not allow fibre DSLAMS in the exchange building due to generated interference that can affect other exchange equipment they have to be in screened cabinets outside the exchange building