The way you describe worries me. If the second email is triggered when another voice mail is left, then it should be a different smart campaign with a trigger that enables to distinguish it from the first voice mail. But you write that you have "a new smart campaign". Only one ?
Pls provide screenshots of the smart list, flow and schedule tab of your smart campaigns.
Sounds like there are 4 trigger flows and the filters aren't setup right in addition that they all trigger on the second voicemail.
Would suggest a different setup, possibly batch flows for all 4 or at least 2,3,4.