I made a payment plan and got denied. Why?

Only the IRS can answer that question.  

WHAT IF I CANNOT PAY MY TAX DUE?

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-payments/pay-taxes/L8aQBCpPO_US_en_US?uid=m9iryksw

Call the IRS: 1-800-829-1040 hours 7 AM - 7 PM local time Monday-Friday
When calling the IRS do NOT choose the first option re: "Refund", or it will send you to an automated phone line.
So after first choosing your language, then do NOT choose Option 1 (refund info). Choose option 2 for "personal income tax" instead.
Then press 1 for "form, tax history, or payment".
Then press 3 "for all other questions."
Then press 2 "for all other questions."
- When it asks you to enter your SSN or EIN to access your account information, don't enter anything.
- After it asks twice, you will get another menu.

Press 2 for personal or individual tax questions.
Then press 3 for all other inquiries
It should then transfer you to an agent.