Quick to sell, difficult to pay for warrantee repairs

So I bought a bakkie from them. Quick to ask for the deposit and make the sale. Signed a 3-month warranty on the engine and gearbox, however, When it comes to repairs on the engine they don't want to pay it, giving me excuses. For weeks I have spent a lot of money on repairs (Still within the warrantee), the owner just declines to pay for the ENGINE repairs as the bakkie has a major engine issue. Showing me that they are trying to play for time for the warranty to expire, However, I have all the evidence on when the bakkie has been repaired and all the communication evidence.