How to complain about RER B train on Friday 1st November from Gare du Nord to CDG Airport

My wife and I encountered a chaotic and stressful situation at Gare du Nord on Friday evening @ 17.50hrs - 19.00hrs 1st November 2019. We were attempting to get a RER B train that we had already paid for by credit card from Ternes to Chatelet to CDG. However despite the fact that we had just purchased 2 tickets at Ternes station we noticed all passengers were leaving the train at Gare du Nord. We got off but did not see any SNCF people to help us. We walked around and asked other passengers and eventually learned that we should go to Platforms 32/33 and wait for a train there. Other passengers there told us that they understood a train would take passengers to another station and from there a bus would take passengers to CDG. We waited for a train and thousands of people arrived on both platforms. Still no train and no announcements or information from SNCF personnel. The crowds were getting bigger, still no trains and the time was now critical for us to leave if we were to make our flight on time. It was incredibly stressful and we went back and forth looking for help but none available so we decided it was best to try to get a taxi. We made our way outside eventually and had to walk a long distance with luggage before we luckily tracked a taxi down who brought us to the airport just in time for our flight. We had to pay €50 for this despite having paid SNCF €20.60 (€10.30 x 2) earlier. SNCF failed to honour their contract with us when we paid for our train tickets. We faced a very stressful situation and had to solve it ourselves by seeking other transport in very trying circumstances and it cost us €50 more. We deserve a refund of our €20.60 and compensation both for the €50 that we had to additionally pay and the failure to honour the ticket contract as well as the stress caused. So how do we complain and seek refunds and rightful compensation.
John & Ann Holian 
Ireland