On final warning for 2 occasions of sickness

I recently had one day off sick as I suspected I had strep throat or something similar(rash, sore neck, fatigue). In my disciplinary meeting following this, I was told I should have contacted my GP beforehand to be signed off. I believe this does not fit with company policy which requires a "fit note" after 7 days.

Because of this one day off (plus my existing 21.77% absence and subsequent written warning due to time off I had for a broken ankle (which happened on site 🙃)) I have been issued a final warning. Meaning for the next 12 months if I have one day off sick I will be dismissed. Anyone else had this problem? It seems lots of people are on warnings for sickness in Lyons Farm Sainsbury's, I wonder if it is a company wide issue.

(For my ankle I was signed off by a doctor the entire time, but during my disciplinary meeting they made it clear to me that they believed I could have returned back to work sooner.)