Affiliation with CIPAV for auto entrepreneur pension

I already asked clarifications previously with regards to affiliation with CIPAV while being auto entrepreneur, please see below the communication just for your reference

Under auto-entrepreneur status, is it mandatory to be affiliated with CIPAV? Would it imply additional social security charges on the top of those that I pay quarterly? I have been under auto entrepreneur status since 2016 and recently received a letter from CIPAV informing me that I affiliated with them retrospectively. For any questions, they recommend to contact URSSAF.

With your reply which was self-explaining:
26 Oct 2017 at 10:44

As an auto-entrepreneur profession libérale, you are already affiliated and paying taxes to CIPAV without realising it.
CIPAV Is the body managing pensions for all professions liberales. The 22.3% rate of social charges that you pay on a monthly or quarterly basis on your turnover, already includes a dedicated percentage for CIPAV. So you have been contributing without realizing.
CIPAV will send you an attestation at the start to confirm that they have you on their records. They will then send you a yearly attestation.

My principal activity as an auto entrepreneur was up to AUG2018 Autres services scientifiques et techniques de conseil n.c.a -
I recently (in august2018) modified my auto entrepreneur activity online to services d’information, traitement de données.  

The new APE code was assigned by INSEE 6201Z programmation informatique , however, it is not exactly what I do ....

Recently, I received a letter from CIPAV saying that I am affiliated with them as EXPERT prospectively (starting from 01OCT2018) and I should pay now 480€ by 31OCT2018.

Can you please explain why they request payments, as I stay in the profession liberale. At least I did not have intention to leave this status; just slightly modified my activity and continue paying 22.3% of social charges. Please advice .