How do I change my auto-entrepreneur activity category?

I registered as an independent Secretaire/Transcriber, working from home, under the auto-entrepreneur scheme in July of this year. I have recently received my paperwork to complete in order to declare my earnings, and calculate and pay my first cotisations. When I came to complete the forms, I realised the category I thought I was going to be registered under was not included on the forms. I went to my local URSSAF office in Angouleme and was told I needed to contact RSI. I visited their office in Niort and they advised me I had been registered as an Artisan under RSI rather than as a Profession Liberales under CIPAV, but they couldn’t tell me why. They suggested I contacted INSEE who had designated the registration category to find out why, and to ask if I could be re-registered under the correct category.

My French is very limited and before I embark on yet another trip, this time to Bordeaux, I was wondering if you could possibly throw some light on to why this might have happened, please? This is causing me a great deal of anxiety as it means if I stay as I am I’ll be paying 23.8% cotisations (including taxes) rather than the 20.5% (including taxes) I expected to be paying. I am also concerned that my cotisations should be paid between 30th December and 5th January, although the lady at RSI said not to worry too much about that.