Unexpectedly high phone bill and payment plan is not an option

I checked the account because I got an email the bill was ready, and it’s almost $700. I did try going through the site to set up a payment plan along with calling them but it’s a few carried over balances.. I was on autopay and the payments were clearing but refunding back to my card as insufficient funds were being detected, it was a confirmed error on their end but they were only able to remove the ISF fees which did not bring the total down much at all.. (Balance now sits at $680)Im on income assistance and only get $800 a month, I simply can’t afford this bill, what do I do?