Banking in France

On 6th May my bank removed 10,000 euros from my current account without my authorisation(they actually duplicated an authorised investment made in April) and since that date have not replaced that sum. I informed them on 9th May when I realised what had happened. I have subsequently filled out forms to reclaim the money. At this point I was told we would share the fees incurred. No we won't be sharing any fees. I was then offered my fees for next year would be waived. I pay my fees in February so no that also is not acceptable. Three weeks ago I was told the process would take 10 days. No I still do not have the money. On Monday I wrote a stiff letter of complaint which to date has been ignored.Is there anyone out there who can advise me what I should now do?