There are so many threads in this forum that deal with the problem of the removal of the first couple of characters, e.g. here:
and if that does not help, use the search function or have a look at the documentation.
That information should help to solve your general problem.
If you need a more specific help, then much more specific information from your side would be required as in such cases, to my experience, every character counts.
I could think of an alternative approach with
$replace(%work%,%catalognumber% ,)
But as you have not mentioned the field names, this is just guess work.