Billing Invoices no longer going to my email

Hello.

Have you accidentally stopped receiving emails?
Also, are you sure it wasn't received in your spam folder?
Did you specify billing contact information on the payment preferences page?
https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/billing-pref.html#invoice-delivery-preferences

If you specify a billing contact on the Payment preferences page, the root user won't receive the PDF invoice or the additional invoice by email.

Just to be safe, I think it would be a good idea to open a case with AWS Support under "Account and billing" and inquire.
Inquiries under "Account and billing" can be made free of charge.
https://docs.aws.amazon.com/awssupport/latest/user/case-management.html