Sounds like you are having the same problem as me. I could get the blade centred on one wheel, but not the other. The manual did not cover this, so I had to figure it out for myself.
The tracking adjustment moves the top wheel in and out. The tensioner adjustment, rather than moving the top wheel up and down, actually angles the wheel up and down. So, unless both wheels are parallel, the tracking is near impossible to achieve.
I found by playing with the tensioner, I could improve the tracking. I did not get it perfect, as I did not want to over tighten the blade. It did the trick, as I have had no more problems since.
Mine was a cheapo piece of garbage. I guess you get what you pay for.