Kent RO — No water pressure after servicing

After routine servicing of the RO plant, during which all the filters and the membrane was replaced along with faulty UV lamp, the water pressure at the faucet has dropped drastically.
After servicing the product should perform better, but it has made it worse, it's probably that the technician damaged the water pump or the hydrophore tank, now on revisit they will make me pay for the parts that were damaged by the technician
How do I avoid this from happening ??
I tried explaining the matter to the customer care, but with no help