Sorry, to hear about the stolen cat; a replacement would be the fix, a good used one maybe hard to find, as they are valuable in the recycle industry, thus the current explosion of thievery and then there are new replacements.
We have found Bosal brand; to be a oem supplier for vw, good quality, no check engine lights, pass emissions testing and are a solid mid priced replacement option.
You can search their catalog for correct part numbers and then search online for best pricing (Bosal brand; sold on Rockauto, Amazon, AutoZone, etc).
So, did you research a new cat and see how much a Bosal replacement would be? If you can afford New, you might post in the classifieds here and maybe someone has a wrecked beat all these would be nice enough to sell you a good used cat from?