You can find your country's embassy easily enough by searching the internet. Some countries, including the UK, have consulates in Marseilles.
British Consulate-General in Marseille:
24 avenue du Prado,
13006 Marseilles,
Tel: 04 91 15 72 10,
Fax 04 91 37 47 06,
E-mail: MarseilleConsular.marseille@fco.gov.uk
The offices are open to the public from Monday to Friday from 0900-1200 and from 1400-1700.,
(Outside normal working hours a consular Emergency Service is in operation and a Duty officer can be contacted by telephoning 04 91 15 72 10.)
The British Consulate-General in Marseille covers the following
departments in the southern part of France: Pyrenées-Orientales,
Aude,
Hérault, Lozère, Gard, Vaucluse, Bouches du Rhône, Var, Alpes-Maritimes,
Hautes-Alpes, Alpes de Haute Provence, Corsica and Monaco