It seems perfectly reasonable to me that you would have a worse performance on a champion you do not know as well as your main. So, I can completely understand why you would be frustrated by teammates being toxic/angry towards you. It's rather unfair for them to blame you, when their bans were the immediate trigger of the situation. Though I'm sure by now you have noticed, that the internet, like life, isn't always fair.
All I can suggest is trying to talk to your team about it in champ select. Maybe even have a link to your op.gg saved so they can see your stats. A little communication in chat that is not something like "wtf are you banning my champ you asshole?!" can go a long way towards helping your cause. Not saying that you said things like that, but I see that sort of thing allll the time in chat.
And, as a one-trick myself, I would give one final piece of advice. Find at least one other champion that you can fall back on. You don't have to like playing them, but if you can play them at even 50% of the ability that you play your main, it's a good place to start. I was forced to do this because Riot decided to do a mini-rework on my girl last season, and she was banned every single match for weeks. So, I had to play someone else. Many people will pick someone who has a similar playstyle to their main. I've been wracking my brains, and I can't really think of anyone who is truly similar to Bard. Maybe try and think about what part of his kit you like the best, and go from there? Whether it's his mobility across the map with his tunnels, the buffed auto attacks from his meeps, his unusual way of landing hard cc. Do you enjoy having a caster with reliable, easy poke and safe cc? If you look for one or two of those things, instead of all of them, you may be able to find a champion that you can fall back on in a pinch.