It is my understanding that Windows XP is not supported beyond version 12.  How can I upgrade to TV 15 and still use the product to support my customers?  
A medical device is FDA controlled and I do not have the legal option to upgrade the customers even if I wanted to.  I cannot use TV if it does not support Windows XP.  I bought a perpetual license years ago, and if I cannot use it anymore it takes a lot of work to migrate to another desktop sharing platform, and I feel that something I bought was taken away from me.  Teamviewer, I want a refund or else the ability to continue on version 12.
I understand there are security problems with Windows XP.  That is not TeamViewer's responsibility.