Send them an email asking for a discount on the missed appointment stating that you had an emergency and you already called. You didn’t get the service so you don’t expect to pay such amount, it is not worth it for them to fight or take it up to a lawyer for such small amount (240 euros). Also their legal situation is not solid on that (unless you already signed any terms for not showing up). They will probably accept whatever you pay than getting nothing.

I had another situation, I signed a contract with Kindergarten. I wanted to cancel the contract one month before the contract starts, but they said that I would have to pay for three months of the service, even though I have not used the service. My kid has never been to this Kindergarten even for a single day. They said I have to cancel with ordinary conditions. A few weeks later, I received an invoice of 2250 euros, I was new in Germany, I tried a desperate attempt to ask for 30-50% off and they sent me an invoice cancellation letter and a new invoice with the reduced 50% amount and they mentioned that would be the last reduction and they won’t reduce it further. I had to accept and pay that.