Oh dear, now the picture is clearer. Did you have the refund agreement from them in writing(email or screen print)? If not, they now can actually claim you voluntarily canceled your reservation without refund and book another airlines.
Funny that you mentioned Aeromexico. Based on my dealing with Aeromexico, they too don't make it easy for you when it comes to refund or giving frequent flyer benefits. Most of their customer service reps seem untrained, and disinterested in customer service.