After receiving the email from Presonus, you only get the free upgrade to Studio One 5 Professional if you purchased within 90 days of the release. For example, I get the free upgrade to S1 5 Pro (or the free year of Sphere) because I purchased on 12 April 2020. Since you purchased in 2019, you're not eligible for the free upgrade. I'm not sure if you're talking about upgrading using your credit card or not though. My issue is that I'm not seeing the "REDEEM" button that people are talking about and I"ve submitted a trouble ticket.
Rock on,
Sin