Hello @Derek Brown
Based on your description If your personal Microsoft account used for Azure Pay-As-You-Go subscription has become associated with another company domain, causing you to lose access to the subscription and Azure portal, here are the steps and options to address this issue:
You can try to switch your default directory to your personal one:
Go to the Azure portal subscription blade directly via this URL:
https://portal.azure.com/#blade/Microsoft_Azure_Billing/SubscriptionsBlade
Use the "Switch Directory" option to select your personal directory and set it as default.
This can resolve the issue where the login redirects you to the other organization's tenant.
This documentation has common scenarios which will help:
I hope this information is helpful. Please feel free to reach out if you have any further questions.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".