I think that the first thing you should check is your payment method for the premium Qustodio membership. Will the membership automatically be renewed or needs this to be done manually? And is the account holder (currently the person who took over your account) able to view your payment information? For example, if you paid by credit card, are they able to view the credit card number, expiration date and the CVV? If so, block your card.
Then you could contact Qustodio using a (newly registered) dummy account so you have access to the contact form on their website. Or you could contact Qustodio by e-mail (
see this page) and explain the situation. Perhaps they can verify that you're the rightful account holder by (e.g.) checking your card, (previous) e-mail address or device connectivity.
If your computer is still under Qustodio control then the account overtaker might contact you later on. If you can't reset your password and the Qustodio software doesn't apply its rules to your device(s) any longer then it's safe to assume that the account overtaker ran away with your account. If this is the case, I hope that you learned a lesson about giving login details to strangers.
Lastly, if the account overtaker has a getDare (or Kink Talk) account then you could contact getDare staff. Perhaps they could be of assistance to you or at the very least, take action against the user account (or make a note of the situation).