Contact
Email robin@robinsingh.co. It is read by Rajvinder Singh, who operates the service — replies usually come within two business days.
For an import that went wrong, include the platform and the username you entered. Those two are enough to reproduce almost every import problem, and without them the first reply can only ask for them.
Faster without email
Cancelling a subscription and deleting an account are both self-serve, and doing them yourself takes effect immediately rather than whenever the mail is read.
Cancel from Manage billing in your account. Delete everything, including your imported games, from your data on the same page — where you can also export your games as PGN first.
Data requests
Write from the address on the account and say what you want: a copy of your data, a correction, or erasure. Erasure is the same operation as the delete button and is not reversible once done.