HELP! was told no termination fee if switch to residential and now I have a $1800 bill in collection

 last year I was told if I switch from business to residential, and i keep phone tv and internet services on residential, they would waive the termination fee.  So I signed up for residential first, them e signed the term agreement to cancel business.  Then i started receiving a bill for BOTH residential and business so i called business support.  The rep flat out said dont pay it.  He went so far as to tell me to cancel autopay and the they would soon audit my account to verify i still have residential service then their adjustment team would remove any amounts owed to comcast business including the term fee.  I flat out asked if my bill would be sent to collections if I don't pay it and the rep said definitely not. I then asked him again and explained that i would be purchasing a home this year and could not afford to have my credit score take a hit if comcast sends anything to collections.  fast forward to now and sure enough i received a letter from a collections agency stating I owe $1800.   I have until 3/1 to get comcast to enter an adjustment and get this removed from collections before it gets reported to the credit bureaus but after multiple calls NOBODY IS HELPING!  supervisors promise call backs then dont call back.  nobody can explain why my bill was sent to collections in the first place even though i was blatantly told it wouldnt be.  This could drop by credit score by 100 points thus increasing my mortgage rate by a quarter percent which would end up costing me OVER $25,0000!!!.  I did every single thing that was asked of me when switching to residential.  If i cant get this resolved asap my only other recourse is to pay $200 to file an arbitration claim and pray I win that verdict