ESA50 extension time for return

hi there, im in the process of completing ESA50 with deadline in two days.
Im unable to complete it by then as im having a episode of actute illness and i wanted to get an extension.

i rang the job center plus who put me through to someone else (forgot who it was .. dont know who im off my head on medication) . they said i had to return the reminder letter in order to get an extension.. is that correct?
Do i need the reminder letter, as
i have had to stay at my partners to be looked after and havent been able to pick up my reminder letter which i guess has been sent to my home address.

im really stuggling atm

I must say that I haven't heard of anyone being asked to send in the reminder letter in order to be granted an extension. On the other hand, I haven't yet heard of anyone has has been granted an extension anyway!