REFUSING TO RETURN FULL REFUND/CREDIT

I Lunga kantolo bought roof building materials from Inyathi Truss in December 2015, delivery was done on that same month. Apparently delivery was done by their supplier on their behalf and on the delivery day fortunately I was there. A guy by the name of Jason was delivering, There was number of breakages on both roof tiles and ridges, upon my inquiry he promised me that if ever the is a shortage I must go to them and collect that number of shortage. Earlier this week I informed Inyathi Truss (David) that the is one pellet of roof tiles left and 30 ridges. When they came to collect they refused to collect or calculate the broken ones whereas, on deliver we both acknowledged them with Jason. I was hoping to get full credit or refund for the whole roof tile pellet and those 30 ridges. I am disappointed because this is not the tone that they were using when they were the ones on the receiving end. can you kindly us me that I get the full refund that I deserve.