Partserve Cape Town can't service my part

I have taken in my Dell laptop and explained in detail everything I have done on the machine already since it is not powering on. This included a new motherboard being fitted already. It was clearly noted that I will pay for any other repair than that on the new motherboard on the document. They had the machine for two days and confirmed they can't find the problem, motherboard (new already) to be replaced at R 22 000 on a machine that costed R18 000. The competitor down the road quoted R 1 500 if they need to work and fix the motherboard. Partserve then realized that they do not have the expertise and demanded R 373. The invoice reads that they can only do test and diagnoses when the new motherboard is in. Very contradicting. I have done more work than them it seems. They even invoiced me for what I told them.