PIP MR extension?

Hiya, I assume that many people need an extension due to disability preventing them from being able to do a sprawling MR letter debunking all PIP’s lies in the full report; I called this morning and asked for an extension and they told me they put a note on the system saying I’ll be submitting it late. Is this how it works? I was under the impression you had to request an extension and they would grant you one. Usually I call once and then call again after and get a completely different answer from someone else to compare. Does anyone know how the extension for MR works? I don’t want to submit it late as I was told to do but then it’s too late and they’ve told me the deadline is over. Thank you