Unpopular opinion - Managers may have a point
Sure you can fight for a job that's likely making you sick, but why? the nature of the job isn't going to change. It will generally always be target driven and force you to put a brave face on things time and time again. I'd never go back, I still have telephone anxiety issues near 20 years later.
Even aside the mental health, If the job is on the phone and you have regulalr ear infections that make that an issue, that's going to be an ongoing problem, isn't it? I'm just picking up one word here, but you say you've been complaining of ear infections, like complaining to your employer? for the line/floor managers, if your quality of work is bad, your absences are bad, and you are complaining about the basic nature of the job, I can kinda see why they are getting a bit exasperated and asking why you want to work there. It's all v well for OH to suggest what would help, but they don't decide the employers needs or available duties sadly.