Microsoft 365 subscription: Which account is linked to it?

I have an active Microsoft 365 Personal subscription purchased through the Apple App Store since three years back. During the last three years, I have remained signed in, but yesterday I had to sign in, and got a message that the outlook account/email adress I provided doesn't exist. I can provide my Apple subscription receipt and transaction details, but I no longer know which Microsoft account the license is assigned to. Could you please help me identify the Microsoft account linked to this subscription? I have messaged Microsoft Outlook but they cannot help me. They have asked me to contact Apple to ask which account my subscription is linked to.