so i just set up my amazon student acc and then i went to amazon instant video app just to see if it works when i signed in said i had to upgrade and that amazon students get half off a membership so i hit upgrade assuming it was gonna tell me how much it was first but nope upgraded right there so did i get charged or am i on a free trial because amazon failed to inform me what i just did exactaly also if it a free trial can i cancel now and not get charged later but still use the service