Maybe you did get burned on this one. If yes, see it as a learning curve, as previously suggested. It seems like you are doing that.
To IDiot’s question, were the terms of payment not agreed upon earlier when you guys negotiated? You mentioned that you guys did put a contract in place. Or was that just an NDA?
Please correct me if I am wrong, but it sounds a little bit like you guys were trying to fly under the radar here. In other words keep the money off the books. This is never a good strategy. Again, if I am reading into things, please correct me. Otherwise I think it’s a good opportunity to generally point this out: Don’t burn the Tax man, keep it clean.
Did you send an invoice a month ago stating that you expect payment within a certain timeframe?
I work for clients in the US, then send them an invoice, they pay, done.
I had to set up my on business in order to invoice the clients for work rendered and to keep everything in order. This gives me now the power to collect interest if they miss the payment or hand it off to go to court should that be necessary.
ps// I understand you are not a native English speaker, but I would recommend a spellcheck regardless. It will make you look a lot more professional.