Enforced change of business regime in France?

I work as an agent commercial immobilier and have been registered since 2013 under the Auto/Micro-Entrepreneur business in France. Without realising it and due to a couple of unusually valuable sales, I exceeded the limit for this regime in 2016. I only found out when régime social des indépendants (RSI) wrote to tell me last month that my existing status had been terminated as of 31 December 2016.

The letter tells me that from January 2017 my social contributions will be calculated in the applicable mode for aem travailleur independant. That was then followed by a letter with a calendar of payments for 2017 consisting of three payments but based on my income from 2015 which was only 11,117 euros. When I went onto my Net-Enterprise account to check whether I could still complete a quarterly return I ascertained that I had to open a new account with RSI which I have now done.

1. What has not been explained is what regime travailleur independant refers to - can you advise what it means?
2. What implications does that mean for my accounting records? Do I now have to retain all receipts and account for expenses and if so what expenses and records need to be kept? I assume I can claim for such things as mileage, fuel, printing and copying but at what rate I know not or what else I can claim for. Unfortunately, because I didn’t realise I had been moved until over three months into the year I have not retained any receipts or mileage records for that period so can you advise if there is a way round that?
3. As last year’s income was unusual and unlikely to be repeated, is there any way I can remain on the Auto-Entrepreneur regime or if not can I go back to it if the income remains below the limit?
4. I went onto the RSI site to make the first payment but when I tried to register the bank account details it won’t let me and instead brings up a message saying the IBAN and BIC was already registered. However, my RSI account does not show any bank account details linked to it so I can’t pay online so I assume it is somehow linked to the Net-Enterprise account but the bank details have not been moved over. I have now sent a cheque for the payment and requested a delay in payment to avoid a majoration but still can’t work out how to register the bank account. Any advice on that welcome!