Unpaid overtime

[stevie21]

I was seconded to a project for the last 3 months of last year and have been repeatedly fobbed off about overtime that I'm due. Apparently, it has to be submitted to the correct person for approval before it is paid. Finding someone who will own up to being this person is proving impossible as a few people from the project have left the company.

Am I likely to get anywhere by visiting the CAB?
I'm not a member of the union and have no interest in joining them.

Any other ideas?