they dont want to pay me

I have been supplying them with fresh fruit and vegetables on a daily basis, the problem started last year December 2015 where they will skip payments, we agreed that payments must be made after within 7days of delivery. since December they where skipping my payments of other invoices, now they are telling me they wont pay me as they have problems with their accountant and I told they I also have workers to pay also pay rent where I store the fruits and vegetables the amount they owe me It can be more than R50 000<br> I buy them fresh fruits and vegetable direct from the market and the is no credit we purchase in cash<br> can you please help me deal with this matter