You are probably thinking of Jehovah's Witnesses but they are not true bible believing Christians. The amount of bible study that they do puts the rest of us to shame but their leaders created their own version. Also they believe that they can regularly be given 'new light'. This means that something that they were teaching people one year is no longer true because God has given them 'new light'
Anyone who has kept old Watchtower magazines will be able to see how the teachings have changed over the years.
Be very wary of them.
I have friends who are J.Ws. and casually know many more. They are all lovely people who are being horrendously misled.