$1800 taken out of my account for mobile data usage

I have been an Xfinity customer for about 8 years. I currently have my internet and mobile plans with them. I have never missed or been late on a payment. I have 4 lines on my mobile plan with the shared 10GB plan. We typically go over a little each month, but nothing crazy. Until last month that is. I have automatic payments set up and noticed that Xfinity had deducted $1819.20 from my bank account.I am just sick over this. I cannot afford to have that  kind of money taken from me unexpectedly  so of course I called them immediately. The representative could have cared less. He told me that my husband and my daughter had used an unusually large amount of data and I was charged $20 for each additional GB. Neither my husband nor my daughter used their phones any differently than they normally do so this just doesn't make sense. Obviously if I had known this though, I would have switched their lines to the unlimited plans and it would have only been $45 each. I was also told that they were continuing to use a ton of data and my current bill was up to $644 (I have switched them over since then) I was practically begging this man to please help me. He said we used the data and there was nothing that he could do. He eventually put me on hold to talk to someone else. When he came back he said he could refund the money and give me a $200 credit and that way I would "only" have to pay $1600. This was not really helping me so I asked to speak to someone else. I was told I would be contacted by a supervisor shortly. When the so called "supervisor" called me back, he was even less helpful than the first guy and said there was absolutely nothing he could do. He said he couldn't even honor the $200 credit that the first person offered because we escalated it to a manager. I was on the phone for 2-3 hours and got no resolution whatsoever. I have since done some research and found that there are a lot of customers reporting sudden spikes in data usage and Xfinity is aware that this is an issue. I cannot believe that neither of the people I spoke with mentioned this or even took the time to see if this was a legitimate charge. Even if it turns out that it was, I would like an explanation of how this could suddenly happen so we can avoid a recurrence of this issue. I would also hope that someone in this company has a heart and can help me reduce this bill. I am legitimately worried about my bank account being overdrawn because of this and then I will have even more fees. Please help me.