Amended 2020 return before due date, with tax lowered balance

Hello TurboTax community,

       I e-filed my 1040 back in Feb owing IRS a tax payment, which I didn't pay at the time. I then received an amended K-1 in March; I e-filed a 1040X on Apr 13th.  According to the amended return, I owe less money to IRS. I sent a check to IRS with the smaller amount based on the amended return, along with the 1040-V payment voucher from the amended return. The check was cashed shortly after.

       Today I received a CP14 note from IRS saying that I owe them money because my payment doesn't match the tax I owed. There is also a penalty and interest charged to me. In the CP14 note, the tax I owed  is the amount before my amended returned. 

      I tried calling IRS but i can't get to a person to discuss this; Also this doesn't seem to fit the criteria of appealing according to what i read from irs.gov. What should I do to get out of this situation?