I think I'm paying for two MS Office subscriptions ($69 each). How do I fix this?

Why do you think this?

How are you paying for them?

If you subscribed directly on Microsoft's website to one, you would need to contact Microsoft to cancel it.

Otherwise, if you subscribed through your Apple ID, you can only subscribe once per Apple ID, so there's no way to have a second subscription active. See here to verify your subscriptions tied too your Apple ID: See or cancel your subscriptions - Apple Support

And check your account with Microsoft directly on their website and see if there's a second subscription active there on your Microsoft Account: https://support.microsoft.com/en-us/help/4522164/microsoft-account-how-to-cancel-your-subscription