WHY IS IT LEGAL TO TEACH RELIGION AS FACT?

When I was a child, the only schools in my area were Church Of England schools, and as my athiest parents could not afford to move house, I went to a Christian school up until the age of ten. Why doesn't the government intervene and make a law to say that you can teach religion in schools, but you must teach it as faith, not FACT? I was taught that I would go to hell if I didn't believe in God, and I was taught that Hell existed. I was very impressionable at that age, I assumed that all adults knew what they were talking about, and that if something was taught as fact, is was proven and true. Why are schools (religious schools or not) allowed to teach religion as FACT, rather than opinion/faith/preference? There are laws saying that if you advertise an mascara, but the model is wearing lash-inserts with the mascara, you must say so. Also, if you provide statistics in adverts and they are proven to be until or pulled out of the air, you will be sued. Why isn't religion treated this way?