I found them trustworthy
I talked to a really niece person that was working for Care on a stand on the street, and decided to give a 20€ donation to their cause. After filling up the long form, I realised that there was only an option for a monthly subscription. I told the person that I didn't want to give more than 20€, and she said I could open the subscription and close it right the next day by calling to Care by phone. Since she was pretty open and nice I trusted her. But later, deep inside me, I thought, what if this is kind of a scam? you never now! But I called next day and everything went smoothly, I canceled my subscription right away and Care didn't even try to retain me with the subscription. So I found everything pretty legit. I take a star out because this process could be a lot easier and more transparent if the one-time donation option was added to the form from the very beginning.