You don't need to spend money on a solicitor for this, unless it was definitely sorted out as part of the divorce and put in writing. Even then, there is almost certainly no reason why the creditor should be bound by the divorce settlement. Legally, as already stated, either of you is liable for the full amount of the debt.
The debt collectors may threaten and bully you - don't let them. You can only pay what you can afford. Get advice from the CAB or any other local free money advice agency, or call CCCS (see website for number). Do not get involved with any fee charging debt advice/management outfit.