As far as I know, there aren’t any Avast Scams.
Your post mentions two possibilities, Dell and iYogi.
It could also just simply have been a cold canvas scam phone call
and they got lucky when they mentioned Dell. Lots of people own a Dell computer.
I happen to own 3 myself.
I would certainly pursue the matter but please, put the blame where it belongs
and that certainly isn’t with Avast.