Why did I receive a CP3219A form after I replied to a previous CP2000 form and agreed to a payment plan?

I received a CP2000 form, agreed to the changes, and signed up for an installment agreement plan, which was approved. 

However, I then received a CP3219A with a tax increase. Why did this happen and how should I move forward? Do I continue paying to the installment agreement plan and ignore the CP3219A form?