Car is going into limp mode because I have recently hollowed the cat

Have recently and most of all stupidly
hollowed my cat thinking would make it
sound abit better well it didn’t to my surprise
cat was good for a week arfter I done it then
engine light came on now when I’m driving
once she warms up it just cuts into limp
mode dosent matter what gear you are in it
won’t rev over 2500rpm any ideas muchly
appreciated??

Have been told it could be the co2 sensors
but have also been told to take it to a diesel
specialist spoke to one yesterday and they
said they could fix it but it would need
-cat delete
-egr delete
- dyno runs
- remap                 For $1595