Cs is partly team dependant, you have to realize that sometimes its better to help your team then to cs.
This often decreases your cs by alot after laning fase. Especially in low elo where players chase enemeis for 5 minutes to get a kill and more bullshit like that such as permanent teamfighting. Your team will often starts fights anyway even if you don't show up causing them to lose in 2v3 3v4 or 4v5 scenarios if you focus to much on farming/objectives.
Whilst it is true that objectives and cs are more important to winning then chasing kills and figting all the time it is often not what happens in bronze/silver. Best tip i can give is pick something with strong teamfighting potential. Champions whom have acces to strong aoe abilities for wavepushing and easy cc to apply will do well.
Just an easy strategy here;

The idea is simple, use zzrot to create map pressure by putting it in a lane behind a tower, the portal will farm and push alne for you, meanwhile you go and be annoying as all hell by goint to a different point on the map and and help your team.
Naut is just as example, but he has real easy cc just auto atatck for a stun ot point and click your ultimate on a carry. Meanhwile you just spam your aoe slow in teamfights and focus on keeping your carries alive, By auto attacking anyone going for them, this stuns them followed by your slow and they should be good, just be annoying and disruptive in fights.
Other easy cc tanks can work too, for example
as support.
Zzrot will help you push/farm and create map pressure drawing enemies away so you can either fight 5v4 and get an easy win. Or your winions push down a tower.
Worst case the opponent wins the 5v5 and your zzrot prevents them from taking objectives because they now have to deal with all the pushed waves.