The bundling is between the office visit and the AWV, not the EKG.
When billing a problem visit on the same day as an AWV, you would add a 25 mod to the E/M charge. It's important to remember that whatever work was done for the AWV should NOT also be counted into the E/M when you level it (such as a portion of the history or exam).
When billing, for example, you would have G0439, 99212-25, and 93000.
When it comes to adding a 59 to 93000, I'm not sure why that would be necessary; there are no bundling edits there. I highly question that because this is a MAC and they SHOULD be following the NCCI edits. Personally, I would ask for documentation from NGS explaining the reason they are not adhering to the edits before I start throwing around unnecessary modifiers, especially a 59.
And it would be correct when billing only an E/M with 93000 that no modifier would be needed.