Lexus V8 developments

On the 13th September 2014 we had a Lexus V8 engin put into our Nissan Hardbody. Was taken back a couple of times because of problems and numerous faults. The last time we took our Nissan Hardbody back was on the 26th of January 2015. On the 26th of February 2015 we got our bakkie back and still our Nissan Hardbody has not been fixed. We have contacted the owner on numerous occasions and still nothing has happend. He has received the full amount and our guarantee is to expire on the 13th of September on the engine. We can't even use the bakkie because of oil leakage,and other problems!