How do I go about getting a refund for a product that is essentially unusable? I just bought Deluxe but it won't recalculate educational interest deductions from the AGI.

Do you mean Student Loan interest deductions? It works fine for that.
But what do you mean by "recalculate"?

I thought buying the upgrade was supposed to change the way it was calculated, thus allowing more of my Residential Energy Credits to be rolled over into next year. But alas, their math skills are not made any better by paying them.

The "free" program calculated AGI without the Student Loan Interest deductions, but subsequently let me enter them. The calculations would not go through on the free version, leaving the AGI exactly the same. I finally coughed up the $59.99, only to be told my taxes were ready to file. Looking at them, I saw that nothing was changed.

https://ttlc.intuit.com/questions/4748299-what-would-be-the-tax-break-for-student-loan-interest-paid

I guess that would be true in theory, but my tax burden remained the same instead of reducing it by $113.00. I know that isn't much, but now I've added the cost of the Deluxe, too. My guess is that it is similar to the lack of functionality in switching to the Freedom Edition (for which we qualify). All my work has to be deleted and re-entered. I chose to spend $59.99 because I am disabled and didn't want to take that time to do something that causes pain, but apparently I would have had to do it anyway. They should not call it an "upgrade" if you have to completely delete everything and start over!