American Credit & Collections LLC bullied into making postdated check Scranton, Pennsylvania

I received a phone call from Heidi telling me I owed $91.67 to Primemed who had givin my account to American Credit & Collections to collect payment.  I told her I was aware of this bill, had  it right in front of me on my desk with bills to be paid Sept 1.  I told her I would call her back on that date & pay them instead of Primemed.  She insisted I had to immediately give her info for a postdated check.  I do not do postdated checks for any reason, I always wait till funds are available before writing checks. I told her I would call on Sept. 1.

The next day, Brandon called, sayng he was from the legal department and the report from Heidi said I refused to pay.  I told him I didn't refuse to pay, that I had the Primemed bill on my desk with the 866-760-6205 number to call on Sept. 1.  He insisted that if I did not immediately give him a postdated electronic check, he would set account up with a magistrate. He became loud & threatening  to report me to a magistrate over & over again. I told him I did not do postdated checks & gave him the reasons why.  

Finally, since I was ill, he was so threatening, I gave in & gave him info for a postdated check.  Then , the next day I received the form letter telling me this company had my account from Primemed.  So I never had a chance to reply to the letter.  Two days later I got a letter telling me I had agreed to the postdated check, that what I owed was $96.67, which is $5 more than my debt.  When I called Brandon he told me that $5 was his pay for calling & talking to me , which he could ask for if he wanted to.  The letter also said payment was due on or before Aug. 30. He claimed to check on the proper information & told me that Sept. 1 & $91.67 was the amount to be paid.   Now, I am nervous, because I don't need an overdrawn fee on my checking account.  Which by the way, he said call if it happened & they would take care of it.  Yes? Am I to believe this??