How did you determine the charge was for Ultiself?
If the charge does not appear as "apple.com/bill" on your payment method, then neither Apple nor your Apple account have anything to do with them.
If it's showing up directly as Utiself on your statement, then it means you subscribed directly with them or on some other platform, probably on their own website and you would need to cancel it through there too.
If it does appear as "apple.com/bill" and you identified it from the list of charges on your account as coming from "Ultiself" , it is possible it's not a subscription, but just a single purchase. Ultiself appears to have individual routines for purchase which have no associated subscription. You may have inadvertently purchased some of those and as such there may not be any associated subscription to cancel, just the purchases. You can request a refund for the individual purchases in that case.
click here ➜ Request a refund for apps or content that you bought from Apple - Apple Support
If you are the Family Organizer of a Family Sharing group, then the subscription if it exists may be on one of the other family member's accounts, and not yours directly even though you are charged for it.
