Since there is no response to this post, should it be posted to a different group?

Please post a screenshot.  I believe you are getting a free update that was included with the program you purchased.  

I have used PeachTree since the mid 80s, upgraded several times. Upgraded to Sage 50 2019 in August 2019. This started popping up soon after installed. I thought it was a free upgrade also but no, upgrade did not work so I called support they said I had to purchase the next version!! And that this pop up would go away. Well it does not go away. I called again, they said no way to remove it.

It is very, very annoying to say the least!! 

Yes, that has downloaded and just needs installed.  Start by installing it on your server machine, then on your workstations.  There is no charge for that update

When I say yes update it downloads the full version on Sage 50 2020 (see image)

Then it wants to convert my data.

Then it asks for my serial number, which i enter my existing serial number, then it fails will not accept the serial number, When I call I'm told it will not work without me paying. even though (as you can see in the image) I get updates until 8/15/2020

Yes, you do qualify for the update and you should not have to pay.  I am sorry someone at Sage told you this, but this is why it is nice to work with a Sage 50 Certified Consultant. I would help you if I could, but I cannot since you are not my customer.

I would call back again and hopefully, you will get someone nice at Sage  to add a 2020 serial number to your account. 866-747-3888.  

Oh, and yes, it will do a conversion. 

Thanks it would be nice to know who to speak to, since in the past 7 months I have asked two people both with the same answer

Hi Playpar, thanks for reaching out. So sorry to hear about this experience. 

I located your account ending in #400xxxx054 using the email tied to your Sage City profile. This account has Sage 50 US 2019 bought at retail with a support plan valid until Aug 15, 2020 as you mention above. I escalated this with Sage 50 US service who managed to get your missing 2020 codes generated. Because your software was a retail package, our system required a manual step to get new codes generated. I've messaged the coaching team to ask that reps be reminded.

If you retry the authentication process now to "upgrade" it should automatically pull the new details. Alternatively, look for an email with your access to the Customer Portal where you can also access your product codes and link to the Sage KB for downloads.

Hope that this helps!
Erzsi