Collection Agency is demanding me to pay for a so-called "unpaid account".?

Read your contract and it will say that you have to pay the early termination fee, regardless of the reason. While your complaints are valid, and would normally be reason to cancel service, unless you have a time period where you can cancel without a terminaton fee if you aren't satisfied with your service. If you are outside of that period or your company didn't offer such a period, you are just plain out of luck. This is why it is important to read your contract, and hopefully, if you do have to pay some money, it will serve as a valuable life-long lesson.