debit order date

i received an sms from that i must fund my source account because the debit order has to run today 17/04 - i signed for the 20th debit order so was surprised , Luciana told me that the terms and condition says that if the debit order is on the weekend or monday they will debit on friday. i feel this is not fair and i have not heard of such t's&c's and asked her for the same copy , she refused refering me to their websites told her i will not be able to.