Not acting according to my instruction

I have an insurance with budget and my debit order goes off on the 20th of each month now all of sudden the debit order went off on the 19th before pay day and it bounced because of insufficient funds,I called budget and a gentlemen by the name of Thomas said it has been change and correspondence has been send to clients which I never received that if your salary gets paid on sunday the debit order will go off before which is saturday I fail to understand Im 20th and if the 20th is sunday my salary will go in on sunday not friday like other private sectors or government now the bounced debit order has caused my account to be red and the guy Thomas said I must change my debit order to go off on the 21 of each month I cannot change it I want it go off the 20th like before or cancell the insurance at get one from anothe company as Im not happy with budget.