Any one with better knowledge should please help me out

Hi steemians, I registered Up to 6 persons last week Monday In my school being 19th February (nine days now) , and up till date approval link has not been sent to there emails not even for one person . I don't know what should be the cause. I even try to re-register them again but it demanding for a new phone number that the other one has already been used. Please help me out with solutions
Thanks