Not so fast. This was a departure from the US. Those tickets are covered by the DOT post-purchase rule which provides that once tickets are issued, no add/collect may be required in order for them to be honored. However, DOT has issued enforcement Guidance providing that in the case of mistake or error fares, no action will be taken against a carrier so long as it makes the passenger whole for any other arrangements he has made and which cannot be dealt with without penalty.
While OP has not suffered any losses such as non-refundable rooms or tour packages, he has lost the ability ---- because he relied on AF ---- to reinstate his BA tickets. This is a stretch, but it is an argument worth making to AF in aid of an argument that AF ought to reinstate his AF tickets, and to DOT when it most likely does not. This is because the post-purchase rule remains in effect and the decision not to enforce against carriers for mistake fares is merely Guidance.
If communicating with AF, keep it short and sweet, explain exactly what you want, and further than you report it to DOT as a violation of the post-purchase rule if it does not do so within some reasonable time period.
Do not bother with any of this unless you are fully prepared to file the DOT complaint.