Let me summarize your problem, as I understand it:
* You are South African and normally require a visa to enter France.
* You will be travelling soon with your British spouse to France and the French embassy is not able to issue you the visa in time for your travel
The good thing is that European Directive 2004/38/EC, on right of movement in the EU for citizens and their family, specifically addresses entering an EU country if you do not have a required visa.
Directive 2004/38/EC
Article 5. Right of Entry
4. Where a Union citizen, or a family member who is not a national of a Member State, does not have the necessary travel documents or, if required, the necessary visas, the Member State concerned shall, before turning them back, give such persons every reasonable opportunity to obtain the necessary documents or have them brought to them within a reasonable period of time or to corroborate or prove by other means that they are covered by the right of free movement and residence.
I expect you will have no problem. The only problem is if the French are on duty in Dover and so the concept of "turning you back" may be unclear. If you find a French border guard on entering France, you may have to explain to them what rights you are exercising (I would guess that would last an hour or so), but I should hope it is nothing that should stop you from enjoying your French holiday.
You will need to be travelling with your EU citizen spouse, you will both definitely need to be carrying valid passports, and you must carry your marriage certificate. (Did you get married in the EU and is the certificate in a major European language?)
You have to be well prepared (with your documentation), and carefully preread the part of Directive 2004/38/EC will allows you to enter France even if you do not have the normally required visa.
I would strongly suggest you take a copy of Directive 2004/38/EC in English and in French. You can find the Directive and related material at
http://eumovement.wordpress.com/directive-200438ec/
Finally you might want to take advantage of the legal advice service of the European Commission
http://ec.europa.eu/citizensrights/ It is free and you can then print the result and take it with you.
Finally, I would always carry the phone numbers of the British Embassy Out-of-hours Emergency Consular Service. Call them if you have a problem which you are unable to resolve with quiet reasoned discussion.
In the event of a serious consular problem, please contact the Duty Officer:
In the Paris Area: 01 44 51 31 00
In the Bordeaux Area: 05 57 22 21 10
In the Lille Area: 03 20 12 82 72 (This is in the area of northern france)
In the Lyon Area: 04 72 77 81 70
In the Marseille Area: 04 91 15 72 10
