Non payment for job carried out

Good day.My husband runs a very small trucking company which he started about a year now,In january this year he did loads for heartland foods.He was given a rate for his loads by the manager,when loads were done they refused to pay him what was due n infact cut the rates to suit them.We had to agree in order to get paid.Its been 2 months now and they still haven't paid him his money.They are a multi million rand company and are giving the hard working people the run about for their own money.We call them about 5 to 6 times a day and still haven't received payment.They are by far the worse company to do cartage for as not only is the boss never around to sort your problem but the staff dealing with these issues are forever making excuses for payment.People need to know what they are and not support them in their products or do work for them as they will be in the same situation we are in