We'd been given a covid response thank-you day off in 2020 in my job which had to be taken by end of March. In January I volunteered to cover a stressful different role the week in which I could have taken the full covid thank-you day off in my main job; the other role is a complex pressured admin job which affects the running of 3 departments which is why no one else wants to learn to do it when the job-holder is on leave or off sick. Afterwards we were so busy in my main job I was only given a half day covid thank-you day at the end of March, which I'd assumed was ok, I could then take the rest of time owed later.
This week, managers said they didn't owe me the rest of the hours as it had to be taken in one go, but they hadn't told me this when I'd deferred the full day off in January. Everyone else, about 18 people, had been given their full day off except for me, because I was being helpful in January.
I've decided I'm not going to help again covering the admin job. For the sake of them not giving me 4 hours remaining of my covid-day off, they permanently lost my good will and there's no one to cover the admin role.