It may have been Chatex if you subscribed to a service that offered access to multiple AI model families in one place.
The fastest way to confirm is to search your inbox for the subject Your Pro plan is ready and look for your Chatex support code.
If you are still not sure, use the support page and choose Billing / charge. The flow checks support code, likely account emails, and then charge details to determine whether the purchase belongs to a Chatex account.