Matrix Budget, the budgeting app from Sky Matrix (Transfinite Technologies Ltd), keeps your figures on your phone.
The Google Play version creates no account. It has no sign-in and no cloud sync, and sends none of your figures anywhere, so there is no account to delete. To remove everything it holds, uninstall it or use Settings → Reset everything.
The direct-download version (sold on skymatrix.biz) can sync two phones. The only account it ever creates is that sync account, and only if you set sync up. The account and its copy of your ledger live in your own Firebase project, the one you created and pasted into the app, so we never hold a copy and there's nothing on our side to delete. You delete it from the Firebase console, as below.
Because the account is in your own Firebase project, you remove it from the Firebase console in a browser:
users, then the document named after your user ID, and delete it with everything under it (state/master holds the ledger, state/devices the device list).Deleting the whole Firebase project also removes all of it in one go.
Email support@skymatrix.biz from the address you used for sync and tell us which step is stuck. We'll answer within a few days. We can't delete the account for you, because it's in your project and not ours, but we'll walk you through it.
More detail on what Matrix Budget does with data: Privacy → Matrix Budget.