Let's say there is a premium product A. It was sold for $$ for few years and then the developer offered the product for free under GPL license for all users and $$ charged if the users need any support from the developer. Few months back the developer of the product decided to sell his company and he sold it. The new owner of the company decided not to give a away the product for free/GPL. So, he again started selling the product for $$ (as it was previously). I have downloaded the product when it was offered for free and am using it. Now, someone contacted me saying I am using illegal version of the product. What I can do now ? Thanks for your help.
It is not a software. It is a php script. other than PHP files it has only readme.txt which says released under GPL. nothing else I have.
If you are complying with the license under which you obtained the product you have nothing to worry about. Someone can't come by later and unilaterally change the agreement you have. If you are concerned ask them to provide the basis for why they believe the copy you are using is not legal. You can tell them if you are satisfied you will cease using it. I do not think they will be able to provide you with any legal basis from what you are describing.