Is there a way to cancel a decision taken during a ''issues''? Because I have clicked by mistake on the wrong option and now my nation has ''compulsory military service'' and I find this totaly useless.
You can check "Require confirmation before passing legislation" in your settings, which will give you a chance to back out of mistakes. Even then, once confirmed, the results will stick.
You'll have to wait until you receive another issue which lets you reverse your decision and abolish compulsory military service again, which will happen eventually but there's no telling when.