debt collection --- mobile company unreasonable charge

A cellular company changed my plan without notifying me. When I found it out, I contacted that cellular company and argued: either put me back to my original plan or terminate the service. I terminated the service on my end, but the cellular company still keeps charging me. Finally, I talked to a high level manager and she promised to remove all the unreasonable charges and the service was stopped before this date since I talked to agents again.

I don’t think this should be something I need to pay for. However, this unreasonable charge went to a collector and showed up today. The incident happened almost 3 years ago. This will definitely affect my clearance.

What should be the best thing I need to do? It is just a small amount of money, but I feel very uncomfortable to pay since I didn’t use the service that was charged.

-If you have no other financial hiccups, and you think that you are in the right (with good arguments, proof…), fight it all the way (up to and including court).
I’ve been in that situation, and I wouldn’t pay $20/$30 as a matter of principle.

-Otherwise just pay it.

Regardless of what route you chose, you need to report it to your security office / customer.