Cannot climb out of Bronze 3

I have been playing, for about 5 hrs straight and I have not won a single ranked game. If I play vanguard I’m blocking 20k damage and going 15-7 most games, if I play strategist I can solo heal close to 16k with mantis and do 10-8. If I play dps it’s moon knight or magic and I routinely go 20-8 ish. What am I doing wrong or do I just need to give up? Advice???