You haven't told us where you are in the world - maybe there is an experienced member close by who could lend a hand.
In my experience with this brand, I wouldn't think it is the blade however, it may be.
What makes me curious is that it has been back to the vendor and is still not doing what you want it to - mmmmmmmm interesting.
Let us know how you go with this one.
Sorry I can't offer anything else.