Lightroom 6 Serial Number no Longer Accepted (Dec 2017)

I have been using lightroom 6 since April 2016. In the last few days, I downloaded Lightroom CC to see if this was better than 6 and if I should move to it, the trial was running till yesterday. Int he meantime I also tried to update it to 6.14 and to my surprise got Lightroom CC Classic installed instead. I did not worry because everything was working (albet as Lightroom CC) up to that point. However, today I decided to uninstall CC and try to reuse my Lightroom 6. Of course it does not work. I have uninstalled and reinstalled it numerous times and also created a new ID and logged in that was and downloaded from the suggestion (other downloads) page but the serial number I have does not work no matter what I do. The develop module is disabled. I have even downloaded and run CC Cleaner tool. I am at my wits end. Does someone else have this problem? Please help. I have paid good money for the standalone version and it should be available to me!