Ask yourself if it is worth the hassle to chase.
My husband had a problem with a client (he is a web designer) who has not paid him since December.
He has sent many emails asking for money, and they constantly gave excuses.
They sent him a cheque with the name of the company mis-spelled so he couldn't cash it.
Then a few days ago, he received a cheque without a signature
He decided that it is not worth spending another minute of his time dealing with this; the time he spends typing an email asking for payment is time that he could spend developing his business in a constructive way.
So he has turned off their website and has sent them an email telling them to never contact him again.
The thing is, if they had been honest with him about any money problems instead of stalling him and sending him bad cheques my husband might have worked out an arrangment with them.