Nissan South Africa please do more to assist me, this has been on going

I have 2017 Nissan Navara. in the past 2 years it keeps losing power and they have been saying DPF has been blocked. In the past 12 months I have to take it to Nissan Mthatha every second week for the same problem. What is worse now is that it has been with them for the past 3 weeks and they are unable to diagnose the problem in their own car. They cannot give me the loan car or hired car. I am suffering for the consequences of their incompetency. Assist guys this is bad for the dealer to be unable to fix their car. It's still under warranty though. S. Madikizela