Manipulation by FNB Forex team

My husband and I had initiated the forex payment from our respective FNB account on the same day and at the almost same time.But FNB gave two different Forex rates for each of us.When we raised a complaint, we don't get the proper response.How can this be feasible to give two different exch rate for the transfer initiated at the same moment.Can someone advise me how to take a legal action on them for manipulating the exchange rate