Failure to meet guarantee

I was sold a DABJETSMART: DABJET 82-0.8kw pump provided on 02 December 2016 (WHICH HAD A 12 MONTH GUARANTEE), It has been faulty off and on 3 months after purchase. The pump has gone in 5 times for assessment and I tried to claim against the guarantee. Their supplier has found many reasons/excuses why my pump does not work...all were clutching at straws.

Everytime it goes in for testing, they say there is nothing wrong with it and must be something e have done, I contests that. They provided us with a loan pump for a week and we had no problem AT ALL, which indicates that the pump I bought is FAULTY. They refuse to honour the guarantee