You have UltimateVotes which has a built-in reminder system. Although this just sends a message, it doesn't fine the user. There's is a developer API so you might be able to use the API to create a small custom feature. Edit: API link seems to be dead...
I think voting should be an optional choice for the players, not forcing them to vote or face consequences. I get messaging the user to vote for the server but fining them?
You can use something such as temporary permissions (using something suck as LuckPerms) give them temporary permission to a command for 12-24 hours, and if they don't vote again, they lose perks. I wouldn't say to FORCE your players to vote, but give them a little perk for supporting the server.
