This does not seem to be correct. The law itself does not specify a specific format nor does it posit a limit on the number of rights exercised per request. Here are some (German) templates which one might use. I'm pretty sure similar documents exist in other EU countries.
https://www.verbraucherzentrale.de/sites/default/files/2019-10/Auskunft_nach_Art._15_DSGVO.pdf
https://www.heise.de/news/DSGVO-So-nutzen-Sie-Ihre-Auskunftsrechte-4429886.html?seite=2
It might be a good idea to send a registered letter with reply advice (Einschreiben mit Rückschein).
Good luck