You can disconnect your Contactually account from your 'Apps & Integrations' page. Hover over your Profile Menu (your name at the top right), and select 'Apps & Integrations'. From there, find the Contactually app, and click 'Disable Integration'.
You will have the option of keeping your Contacts and Buckets, or removing them from your rezora account. Select the appropriate options of your choosing, and click Save.