Best thing to do is write a letter/email someone higher up and explain what has happened. They'll probably apologise and throw some vouchers your way.
Some people post on the company's twitter. This works well for both parties as the matter is acknowledged and resolved quickly (before a news site picks it up) and the company is seen as caring for their customers.
Lawyers - forget about it. Your time and money are better spent doing literally anything else.
Well not sure how newsworthy this will be, then again depends on how desperate they get.