Work problem!

I had breast preserving surgery in January and then had to have sentinel lymph node removal at beginning of March. Doctors gave me a sick note until 31st March. Had been off work since January, wasn't in the right mind as work in school. Head text me on 12th March to have a case review and offered to have on the phone due to covid. She asked when and I said anytime. I didn't hear off her and then schools closed the following week just open to key workers. All staff got email to give us the choice to go in or not. I replied and said due to recent surgery I didn't want to put myself at risk. I text head to tell her my tissue had been sent to America for oncotype dx testing and might need chemo then radiotherapy. Luckily no chemo. I didn't renew sick note as in effect I could have been back at work waiting radiotherapy. Other members of staff have just decided not to go in and in full pay. I got a text this morning saying hr were sending me a letter re sick pay. I told her all the above and she said I could get my sick note in at anytime I said but I'm off because of covid not cancer and just I would maybe need time off for radiotherapy. She has got back to me and said did I have meeting with OH I had to cancel twice due to surgery and they didn't get back in touch and I guessed due to covid. She said she is passing everything to HR as she didn't think I could return until treatment is complete and I would need meeting with OH too. Also need risk assessment etc completed before I can say I'm fit for work even if closed! I told her I believe if waiting for treatments and feel OK I could return. Full pay stops end of June and might go to half. just annoying others are getting full pay until they go back or even working one week in three if I was OK I would have done! Any advice please thanks in advance