I understand your being upset at the error and big bill.
I want to make sure to separate the term "contract" from "Next installments". They are different. Next can be paid off at any time, as in the photo I posted. A contract cannot. Contracts are not listed separately as Next is, and are tied to the line of service. The only way to "pay off" a contract is to cancel the line and incur an ETF.
The only way to reverse that is to add the line and contract back to your account, which you can still do.
With that information in mind, did you have a contract or Next installments on each line?
If you had Next on one, and a contract on the other, it might explain why you are in this position now.