The problem with your circumstance is that a Chapter 13
postpetition debt can only be added to the bankruptcy plan if the creditor files a proof of claim
. The debtor cannot force a postpetition creditor into filing a proof of claim -- neither can the debtor file the proof of claim for the creditor, because the creditor can object to the claim as a means of maintaining the postpetition debt.
The only way out of this during your Chapter 13, in my opinion is to file an adversary proceeding and prove that you do not owe the debt at all, because the creditor has created a fraudulent debt as a means of protecting itself.
Alternatively, you could wait until the bankruptcy ends and the creditor tries to collect in state court, at which time you could counterclaim or defend that the debt is a fraud.
Or, you could convert to a Chapter 7
now, and that would include any and all of your postpetition debts.
Those are the options. There are no others that I can see.
Hope this helps.