2nd cat going in for 3rd in space of 1yr?!?

Hi all

I am hoping one of you kind people could offer me some advice....?
I have had my 2005 td4 for 2 years now and replaced the catalytic convertor last July due to some corrosion. 3 month ago max the new cat collapsed so we had it replaced under the 2yr warranty. This week it has collapsed again and has not even covered 4k since the first replacement in July. So I went back to the garage today to ask them to look at it and they said that if it has collapsed in such a short space of time they would not replace it at there is obv something else wrong with the car to cause it, my question is, do any of you guys have an idea what could have caused this and what I should do? Btw the garage has since agreed to replace the cat again. The car is serviced every year. When I open the back window there are strong fumes coming in but it doesn't smoke.

Seems to me the replacement cat being used is of inferior quality !

Ha that's what we thought too.....but just wanted to see if anyone had a similar exp.

I replaced my exhaust last year , but found my original cat was ok , and managed to source a mid section without the cat from germany ! Hope you get yours sorted !