I found your two recent support requests, and will answer one of them, but I’ll also explain things here for the benefit of other people who read your question.
In Feb 2019 the two subscription products named SketchUp Pro and SketchUp Studio were introduced. As part of the naming of the subscription product as SketchUp Pro, the existing permanent license (meaning that it continues to work even if you stop paying) was renamed to SketchUp Classic. Your old SketchUp Pro license is now referred to as a Classic license.
To check on the state of a Classic license you would visit this page, enter the serial number for the license, and the email address that is on the license:
You can try that on your license, and see that you didn’t renew support when it ran out on August 5th. Not having any support may be one of the reasons your support request hasn’t been answered yet.
If you want to check the subscription products that you own, you would sign into this page:
In your case you will only see the SketchUp Free subscription product, because you have never bought a subscription version of SketchUp. If you did the 30 day trial of SketchUp Studio, that would show on that page as well. If you were to migrate from a Classic license to a subscription, your subscription would show on that page.
For the migration offer email, it is telling you that you can use your existing Classic license as a way to get two years of the newer SketchUp Pro subscription, for $240 instead of $598 (in £ for your case I believe). As your current license isn’t under support at the moment there isn’t any hurry. You could get that same discount up until April 3rd 2021.
Your current 2020 license will continue to work, whether you migrate or not. But, you have another option, for the next few days. On that Classic license manager page you will see that you could get your existing license support reinstated, for a $60 fee. The normal yearly support amount is $120, so the total to get back on support, and get the next 12 months of updates, would be $180.
If you did that you would finish the next 12 months with a permanent license for the latest version of the SketchUp desktop applications. You could then still take the 60% discount offer to give you a subscription that would run from the end of October 2021 to the end of October 2023. After that you can decide whether to renew the subscription, or to return to your most recent permanent license.
Having typed all that up, I think I will reply to your support email with a link to this post! If you need to reply with specific personal questions, make sure to reply to my support email. If you have general questions that might interest other people, you can reply here and I will answer here instead.