So I'm no GM, but I thought I'd give my two cents as someone who knows that feel. I've always been gold, dipped into silver a couple times, and I was so discouraged that I was actually convinced that I would never rise above gold. Been playing comp since S1, and this season I hit plat for the first time - within a week - after barely placing gold. As of this post I'm 24W-9L in comp. I thought I'd share what I started doing differently:
Committed to a role, or two. In my case, healer. This includes figuring out each healer's strengths and weaknesses, what good positioning means, and knowing when to pick them. If I'm Zen, it's usually because we need to focus discord a Pharmercy, or burn tanks, etc. The same goes if you're DPS, you have to know why you're picking Soldier (take out the Pharah) over Pharah (they have no hitscan), and what "doing your job" actually means. I know everyone wants everyone to be flex, but in truth good flexes are few and far between, and I'll take a confident tank over a sub-par DPS who's just trying to fill a role they're not good at. So, I'm honest with the team: heals are my strength. So far, I haven't had to not heal and it's worked out for me.
Tweaked my settings. After reading recommendation after recommendation to find mouse/control settings that work for you, I finally gave it some serious time and effort finding what works for me per hero. Sensitivity, hero-specific controls, the like. Made the world of a difference.
Evaluating plays and team fights. I started really trying to figure out the whys: why we lost the point, why we rolled the enemy team, or how we could have contested better. I'm talking the precise sequence of events per play/fight, and this goes beyond pointing fingers (this is sadly the knee-jerk reaction, in my experience). Getting into this habit helped me to understand my role in team fights better, get my timings and placements right, and it even improved my call-outs significantly.
Keeping track of enemy cooldowns, especially ults. Baiting hooks, baiting Mei walls, watching def matrix, and keeping track of time + enemy performance to see who is likely to ult next. I've often been able to predict ults, calling them out 1-2 seconds before they happen. It's helped me save myself and teammates from getting picked, and it's helped me survive through very aggressive engages. These little things help win team fights.
Basically, it occurred to me that that my definition of "doing well" was misguided in previous seasons, because I was focused on my individual performance instead of on my role, my job, relative to each game and team composition. I realized that every sub-optimal decision had a cascade effect that could have cost us the team fight, and ultimately the game. There's a lot I couldn't control, but what I could, I tried my damn hardest to.
Anyway, I don't know if this helps at all or if it just sounds like meaningless rambling, but I hope you don't get too discouraged. Good luck!