IOS deleted all calender events future and past back to 2016, How do i recover all thats lost?

Yesterday, my calendar was working normally. This morning, it seems to have reset back to 2016. There is nothing after that. All old monthly (bill/medication) alerts from back then that are wrong now are in place.

I have serious medical appointments, visit 4 different hospitals, therapy appointments, all gone. I often need to check in appointments when I had this scan, that test etc because it's quicker for me to use the calendar search than the Dr finding it on their computer (not that all hospital records are even linked) and now it's all gone, 8 years of past medical appointments, and future appointments (I'll have to email all the hospitals to see when I'm due there next)

I've obviously googled fixes and nothing's working. I pray someone here can help.