To be sure I wrote them an email at the same day of booking but did not get an answer quickly enough and decided to call the German office. Herr Lucas Sailer apologized for not being able to handle my request due to offline issues and told me he will call back. This never happened and when I myself called again in the evening was told that the car indeed had limited miles and there is a cancellation fee if I canceled.
After this conversation I made myself informed and checked the cancellation policy in their website. It clearly states that there is no charge. I took a screen shot for proof.
I canceled the car and was reimbursed the charge of the reservation immediately automatically by the mother company in England.
I am getting then a very unprofessional unsigned email in German that my credit card will be charged unilaterally the cancellation fee told to me by phone. I answered this not to be authorized as the policy is indeed no charge in case of cancellation and warned them that I will ask my credit card company not to accept this charge.
Yesterday I found the charge for cancellation in my credit card. It is unauthorized and therefore fraudulent. Watch out dealing with this portal.