How high are you going?
Are you just trying to contact you local rep, or some one further up the chain?
My local union rep is useless, so we often end up going to Branch or regional rep (never had to go to HQ.
Occasionally we go sideways and enlist the help/advice of the rep from one of our neighbouring offices.
I think my union also has a legal advice line (thankfully I've never had to find out for sure)

Have you exhausted all these options? as a fully paid up member they should be providing you with all the advice and support you need in this situation.

Failing that, get yourself down to the CAB.