I had 50 credits which were paid. I stopped my subscri to find out that I lost all my paid credits

Yes, by cancelling your stock subscription, you lose all your unused plan credits. It's well documented and even, when you cancel you get a warning for this.

Just stopping the payment does not stop the subscription. You really need to cancel that one. To cancel, you need to go to https://account.adobe.com/plans and manage the plan you want to stop. To cancel without paying the early cancellation fee, you have to cancel in the last month of your subscription. The early cancellation fee is half of the remaining dues, so it's cheaper to cancel when you do not need the service any more, than to wait for the end of the subscription.

To contact Adobe Customer care: Adobe customer care can be contacted by beginning a secure chat session at https://helpx.adobe.com/contact.html?rghtup=autoOpen. Pop-up blockers need to be disabled, you need to accept cookies! If the chat window fails to open, or is non-responsive, use a different device and/or browser to start the interaction.

For support via Twitter:
https://twitter.com/AdobeCare

(see also here: https://community.adobe.com/t5/creative-cloud-services/how-to-contact-adobe-support/td-p/11875703 or here
https://community.adobe.com/t5/account-payment-plan/how-to-contact-adobe-support/td-p/11843852)

Important: Adobe does NOT contact you unsolicited by e-mail or direct message. If you get contacted by direct message from a person, claiming to be an Adobe employee, look at that profile and check if they bear the “Adobe Employee” marking under their name. Adobe support does not use Skype to give you support.
If in doubt, ask the forum.