Pls somebody should help, have been trying to pay for Facebook ads but its rejecting all the Debit card am trying to use in paying for it, what could have been the cause ?

Sir send a review to their admins that might help . . You can also check www.techsload.ga for other interesting post

I do use my diamond bank debit card to run facebook ads so I think you just need to change your card use another

Your problem is really not your card .I noticed this same problem too .
So what I did is add myself as admin of the page (My second facebook account )
Create a new ad profile and make sure you select Nigeria as your country and Naira as your currency
Then boost the ad , it would ask you to fund your account immediately , choose the amount you want , any card would work since the denomination is in Naira .