I studied that religion. The young priest guy I studied with agreed that we are no longer under the old law/covenant, except for the Sabbath Day. But the new testament says if you obey a law you must obey all of it- therefore you would need a 2,000 year old high priest to to sacrifice to atone for your sins. And that would be an insult to Christ who is now our only High priest Who sacrificed once for all. According to Romans 7:14 and Matthew 17:1-5 just like in a marriage, following the teaching of Moses and Jesus would be committing spiritual adultery.
Also, he said God never intended man to eat meat, yet God commanded it in Deuteronomy 14:23 that His people eat from the herds and from the flock. Jesus, Who never sinned, kept and fulfilled the old law- and this was part of it- therefore Jesus ate meat.
You are correct in saying there is only one true church, but SDA just doesn't match the bible. I know it is a hard thing, but think about how many people were born and raised in false religions, and the odds of one of them being right that theirs is the one true church matching the bible are not good. We must all compare our church to the bible to see if it matches- no matter what others say or how you were brought up.