If there is a COA on the case for Vista, in what way does it not 'do it'?
also "Tried phoning up but after a lengthy session it didn't work" could do with more explanation.
The only way to get a fresh COA is to buy Vista Op Sys. If the COA key on the case is for Vista there is no reason that it will not 'do'
Are you sure you entered it correctly, it is easy to mistake a 0 for an O and B for 8
Perhaps it would help if you gave us a more detailed description of the problems encountered.