[keikobadthebad]

Check your contract, it will usually say disputes have to be performed in Germany.

It just doesn't sound like there's enough money at stake to pay german lawyers, manage the case and come out ahead even if they pay.

You can try a place like this (just a result of a quick google, no idea about them) https://www.bierensgroup.com/en-gb/debt-collection-germany/

Getting chased up in german, from germany, in the correct form might panic them into paying.