Barclays finance

I got iPhone 14 pro on finance and the direct debit is due to take tomorrow although it’s not showing the amount in the direct debit - some direct debit’s fail to be taken from my account others seem to work.. I was going to see if it gets taken tomorrow if not will ring them and make a payment over the phone, after explaining the situation and giving another direct debit account to try.. would it still be on the same date the direct debit? If use another account and will I occur a late payment charge? I don’t know how long the money I pay tomorrow over the phone will take to process? Also what reference number do I use? Because it states it automated??