For me that sounds like scam or blatant lie.
As a first thing: no German court can sentence a foreign ISP to divulge any information.
2nd: there is no real High Court in Germany, the highest court in Germany is the federal constitutinal court - and that is not allowet to accept a claim from a p2p company. So the next highest court (for civil and or criminal law is the "BundesGerichtsHof (BGH)" but they cant take a claim with a the value of £ 500 - that value has to be decided by a "normal" court (Amtsgericht).
3rd: there is already a sentence (of a federeal state's upper court, IIRC Berlin) which allows a state lawyer to dismiss a claim that aims to get a Internet users personal data from an ISP by a criminal claim (only way to get a court order to divulge that information legally) only to start a civil claim from that data.
There seems to be something terribly smelling about such detours.
I can only advise each of our users who gets such letters to search legal advise - please remember - I am not a lawyer and I'm not allowed to give legal advice.