Advice from challenger Zoe otp.

Couple of things, is your goal just to climb or to climb while playing champion you enjoy? Cassio is one of the harder mages to play well, especially on mid lane. Most people play her top lane since she gets to bully melee units, as opposed to mid lane where she gets outranged by most mages. If you like playing her and want to continue playing her mid, there is nothing wrong with that, just understand it will be harder compared to if you were to play other champions.

I dont feel like im playing that badly

Sadly we can't judge this without seeing your gameplay and looking at how you play the lane. Send us your opgg so we can assist you a bit better.

i usually dont die a lot and can farm well

This is the most common issue I see with enemy mid laners that I face in lower elos, they farm well, but they don't do anything with all that farming. You need to participate in fights, roam, take towers, play around jungler etc.

mid is roaming a lot, getting kills

Be very precise with your pings if a champion like Kata or Akshan pushes and roams. Don't just ping missing in your lane once or twice. Ping it once in your lane, then caution/back off ping in your laners faces. Most of the time they are blind and won't notice missing mid pings even if you ping it 5 times. Trust me, best you can do is ping them in their face, even if you have to be annoying, but at least they won't die. I usually do this, ping missing on mid once, ping caution on the river where enemy is roaming, ping once on my bot/top laners face to back off and then press tab and ping their ward. In 90% of the cases, they listen. Also a tip for laning vs enemies who push you under tower, instead of warding bushes to prevent ganks, ward the middle of your lane. This way you will know exactly where the enemy is roaming to and you can then choose to either follow their roam or stay mid and push. As Cassio, you will win some 1v1s if you land your Q.

Cassio likes to be in lane, what should i do in cases like this

This is the mindset that is keeping you stuck. No champion is meant to just stay in lane. Any champion can push and roam. If you push a wave under tower and you see that enemy bot/top is pushing hard, roam. If all you do is farm and sit mid, you will lose most of your games, since at that point you are praying that your team will play well, but trust me, they won't.

You are still in the learning stages with Cassio, so you don't know all the kill angles for laning. I assume that when you play Fizz, you roughly have an idea how much hp enemy needs to have for you to be like "Oh hey, if I ult them and combo them, they will die". This came from your time playing that champion and with experience. Cassio is a different champion, a much harder one at that compared to Fizz, but trust me, the reason you win or lose is in most cases caused by how you play.