If you experience online orders being duplicated into your POS, this is due to internment connectivity issues.
This happens when the Orders2me agent that's installed on your server PC assumes it passed through the online order but it didn't receive a confirmation back from your POS with an Order ID associated so it sends through the order a second time.
I'd suggest setting up a Network Monitor utility that runs on your server PC to help you pinpoint such connectivity issues in the future.
You can look online for a tool or install something like https://netuptimemonitor.com/