Parallels desktop is asking me for my old key, but I do not have one.

I previously used the free trial version of Parallels, I have recently purchased a new Key and have
Parallels Desktop 18 for Mac Standard Edition, Permanent Edition. I've been trying to sort this out for days, using every option possible! I paid 54 pounds for this key and I can't use it it's extremely frustrating. When I get to the screen to install windows through Parallels I enter my purchase key and click Activate, it then asks me for my previous key which I do not have. I previously used a free trial version . If this is not sorted I want and expect a full refund! thank you

 

Hello, please be informed that if you have purchased upgrade key, then you have to activate along with the previous license key. If you do not have previous key, then purchase the full license key instead of upgrade key, and we will help you to get the refund for the upgrade key. thanks.

 

Please I have same problem so can u explain how you will help me to get the refund for the upgrade key, thank you