IRS sent letter terminating my installment agreement

I received a letter from the IRS saying they intend to terminate my installment agreement. The Form is called a CP523. It said I had missed a payment(s). It says I have 30 days to respond, either send the past due amount or we will terminate your agreement. However, it also says to call them and they will see if they can reinstate it. So, have they terminated it or not? I called them this week and the IRS rep said I was fine and I just needed to send my most current payment. He put me on hold several times checking on it so I am kind of worried. I did call in the past due payment but am not sure if this takes care of it. As I said, I did call them but the rep seemed to be unaware of any problems with my account. I would like some advice from someone who has received one of these CP523 letters. Thanks.