have there been any problems with the catalytic converter, e.g. plugging>

What is your question?

There has been a "no start and stalling problem" with my 2008 Touareg that was not fixed with a fuel pump replacement as recommended. Now a VW dealership in TX is saying that there is a plugging problem in the catalytic converter that can only be remedied by replacing the catalytic converter, for an estimated cost of $5000-6000. Please advise. Note: I've been advised by a VW dealership in FL that VW issued an extended warranty on its catalytic converter (10 year / 150k miles) while a local VW dealership in CA says this is NOT so. ????

What makes this problem better or worse?

nothing that I know of.

How long has your 2008 Volkswagen Touareg had this problem?

since May 2017