My new Apple ID is working for purchases but not updates. What should I do?

I recently changed my Apple ID to make it more secure because several emailed receipts from Apple had been deleted without my knowledge. My new Apple ID is on my account information page as my primary email address and is working for new purchases. However, when I try to sign in to download an update from the App Store, my old Apple ID comes up and is 'greyed out', meaning that I can't delete it and replace it with the new one. Nothing happens when I click on 'forget'. If I type in my new password, it just says that my Apple ID or password was entered incorrectly and does not give me the option of typing in my new Apple ID. Can anyone tell me how to fix this extremely frustrating problem?