Can’t sign in

You would need to speak to account security regarding recovering an Apple ID.

If you forgot the answers to your Apple ID security questions -

https://support.apple.com/en-us/HT201485

Apple ID Support -

https://support.apple.com/apple-id

World-wide Apple Support -

https://support.apple.com/en-us/HT204169

Support by phone, email or chat -

https://getsupport.apple.com/

Apple Support by Twitter -

https://twitter.com/AppleSupport

iTunes Support form -

https://support.apple.com/en-euro/itunes-contact

You can't combine Apple IDs. This may be your basic problem. See If your payment method is declined in the App Store or iTunes Store https://support.apple.com/en-us/HT203005.

You can get Apple telephone support  for help in solving your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362  Be patient sometimes Apple support is closed to immediate phone support.

And here is how to contact iTunes worldwide support via text or chat using this link https://support.apple.com/choose-country-region/itunes After choosing your country, see the heading Tell us how we can help.

Bad idea. You've now abandoned everything you've acquired in the other Apple ID, free or paid. Apple will not combine your IDs and will not transfer content from one ID to another.

ASC - Late 2012 Mac mini, macOS 10.15.5; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.5.1; iPhone 8+, iOS 13.5.1; TV 4th Gen, tvOS 13.4.6;  HomePods, audioOS 13.4.6 and Airport Express w/ Airplay 2

What happens when you try to log in? Error message(s)? More information would help.