I disabled the Insufficient Bandwidth alarms on my systems. If there's really a problem, you'll know soon enough.
As to digits being recognized by voice mail, there aren't a lot of adjustments. You used to be able to adjust all sorts of DTMF settings, but not any more. I digress.
Go to Voice Processor / Timers and Limits / DTMF Detection Information. Most of the settings will have a red X, meaning they can't be adjusted. Press F1 and review what the remaining ones do, then experiment with settings.
Warning - take a screenshot of the default values, so you can revert back.