If you really need to fly on a date other than what they are proposing, and can't get them (by phone, I guess) to relent, then beware that if you go ahead and book your own replacement flight, the interpretative guidelines effectively let them off scot-free, and they won't have to reimburse you any extra monies incurred in the cost of that flight above the reimbursement of your cancelled ticket.

Perhaps if you have travel insurance, this is something you could claim on as regards the extra costs necessary to cover any new ticket you arrange yourself.

As regards claiming the re-imbursement of the cancelled flight, and the cancellation compensation, you should be able to secure this yourself by following their complaints procedure. Be prepared to be knocked back - it's the default approach by many airlines, knowing many will just give up. Either write a letter or send an email or use an online form - whatever they specify - and keep the letter short and factual. Refer to the specific articles here; perhaps include the interpretative guidelines too.

if they turn out to be too much hassle to deal with, you could investigate using one of the various claims agencies that have sprung up. Some that I have used won't deal with airlines based in some countries (as they may not have an office/solicitor in that country to write the letters that spur the airline into action) but you should find one that will deal with a US customer and a French airline. Most will take a cut (typically 30% or more) from any payout.