Facetime not allowing me to answer or make calls

Dear apple, I was able to make 2 facetimes earlier,, then in the afternoon i tried to make a facetime call , it rang then as the person tried to answer it immediately hung up and said call failed , once i attempted to make a call it rang then immediately hung up and said call failed , i have a great internet connection, i went on settings to make sure facetime is on (it is).this is my iphone 7 , my sister has the same exact phone and is able to make facetime calls. Pleaseee helpp