You offered the GPLv2, so they are free to use the GPLv2. A license cannot retroactively take away rights it already granted (and should not, because people might depend on them for good reasons). And if it only gave lime-limited rights, it would not really qualify as free software licenseÖ
I would love if somebody could explain what would stop the evil company from doing that.
//EDIT: On the other side if some hole in the GPLv2 gets found and you want the new GPLv4 to apply cause it fixes that hole, who would win in court? You that chooses the option of GPLv4 or some evil company that chooses the option of GPLv2 (cause they simply don't want a later version) to exploit that hole?