Change of debit order date

Service was bad i phoned in to only change my debit order date,im not working at my old place i have a new work place where i work,so i was told i must send in a copy of my I'd and prove of my payslip that im gonna get paid at thee end of every month i ask them to move my date to the 2nd we get paid on thee end of the month or the 1st of every month is not like im telling them im not gonna pay them i pay them every month on time but now when i want to change my debit order date its a big thing