I previously purchased Alerts Pro 2-0-4 and Pro Likes Mod 1-3-8. I recently update my SMF version to 2.0.13 and they are no longer working. Should I buy new versions? Have these packages been updated?

Those versions are quite old, I'm not sure if they can work fine with 2.0.13, but it's entirely possible, maybe the upgrade wasn't property made, try re-installing them, if that does not work then you would need to upgrade both products (Likes is already on the 2.0 branch, so it's quite different).

Thanks. Do you have upgrade prices or do I buy the complete new versions?

From the client area you can do the upgrade which has special prices