If you're European, frame it as a GDPR issue. You have the legal right to correct your information. Mail dpo@facebook.com, asking them to correct this, explain

If you're European, frame it as a GDPR issue. You have the legal right to correct your information. Mail dpo@facebook.com, asking them to correct this, explaining them you have tried normal channels, and reminding them they have one month to reply. Failure to do so means you can lodge a complaint with your local data protection instance.