Can I contact a Uni if I don’t meet the grades due to a long-term condition I have?

If I fail to meet the grades on my conditional offer as a result of an illness that took me out of school for a number of weeks, then extra time because it was a long-term condition (so I missed a lot of school), should I contact the university when they reject me?

I think I only missed one grade, but it will probably be by a lot. The subject that I am applying for is predicted to be on target and so is my second A-Level, but the third I don’t think I’ve reached.

If I should contact the Uni, should I get the teacher of the subject I’ve applied for to call the Uni, or should I do it, or should we both?

I’m not confident it’d change anything— but I do want to try if I can because I did almost die and missed a lot of school to recover.