>Perhaps someone can give me a little advice on how they would handle this. In my 21 years as a programmer this is the first time I have experienced this.

Twenty one years as a contractor? I bet not, because in that case you were able to manage extremely well, in regard to this aspect.

As a contractor you MUST have a lawyer, and you MUST be prepared to spend some money to check contracts. This 'some money' will ensure the 'big money' that comes when you do well what is agreed upon in the contract.

In your specific case, agreements in e-mails might be enough for a lawyer to go to court. It is enough these days, although it is not as solid as signed papers.

One warning, however. Going to court is very expensive. That's not a problem if you can afford it and if you win, because the losing party will also (likely) have to pay those costs. However, it may be the case that the client is about to go broke, without that you know of this, and that the bankruptcy happens a week before you would be in court. In that case, you can even say goodbye to the money you spent on the law suit. The chance that the client does have financial problems is quite big, because else paying you would probably not be a problem.

All things I said here are applicable in Holland, and things may be different where you live.