Data OVERAGE??

I have been an Xfinity customer for over 7 years and recently I bought my own equipment. Since I have bought this equipment, I have received an overage notification 2x out of the 3 months that I've had the equipment. I have called several times trying to get this figured out. The offshore rep that I talked to this am would not allow me to speak, everything I said she spoke over me and was yelling, then straight hung up on me. ( WAY TO GO XFINITY CUSTOMER SERVICE) I had to call back and talked to a 2nd offshore rep for a little over an hour, this is just today, she told me that since I use my own equipment that they can only guesstimate how much data I'm using. However, if I started using xfinity's modem that I most likely would not go over on my data for $14 a month. I have been tracking my own data since I bought new equipment and I'm not even close to being at 1.2 terabytes. I was told I was not going to be charged and yet here we go. I am being charged for data overage. I have been checking my data daily/ monthly, I have not gone over on data, NOT EVEN CLOSE to 1.2 TB but Xfinity does not want to hear this. They want me to upgrade to unlimited for an extra $30 a month. I refuse to upgrade when there are 2 adults that live in this household, We both work a full-time job so we are not home until the evening and on weekends we do not stream a lot and basically just use our cell phones that are not on Wi-Fi... I have also contacted your customer assurance team with no luck, so please don't ask me to contact them again. Contacting Xfinity is becoming a full-time job for me, and I absolutely hate speaking to Xfinity CS. 

Looking at this forum it seems Xfinity is having a major issue with this. Seems a little shady to me.