Membership Pro membership upgrade and prorating not working

The website I'm working on has multiple membership options - two of which are a monthly and an annual subscription. I have the pro-rating add-on installed so users can upgrade from the monthly to annual subscription. The idea is that after they sign up for the monthly, they're given an upsell to enroll in the annual. In the annual subscription, I have the upgrade path for the monthly set to cancel and prorate. The issue is that it's not cancelling the monthly subscription and the cost isn't prorating. I've tried every possibility with settings and it's just not working. Any ideas?