This is definitely something I'd need to do a bit of investigation into before I could answer with confidence. Certainly, I understand getting a notice that you're being charged overage when it appears you're under your usage is distressing. I do apologize for that. Please allow me clear this up for you. If there's a technical issue causing this, I can make sure it's fixed and the charges are reversed.
Please PM us @CommunityHelps so I can look into this matter for you. If you're not familiar with our PMing process, you can find instructions here.