One thing to keep in mind with rechargeable Lithium batteries is that if they are left uncharged for extended period of time, as I mentioned, they tend to lose their ability to be charged again, or at least, not fully charged.
Two months may not be an issue, unless they were completed discharged. Since you have already tried resetting them and you are still not seeing any sign that they are charging could indicate that their batteries may now be defective. Apple does offer a service to replace these batteries for you and I don't think it required that you purchased them directly from Apple.
Ref: Beats Repair & Service - Apple Support