Bad Service - Debit Date Change

Not happy at all with their service and explanation. I have to change my debit order date from the 15th to the last day of the month. I was debited a full amount on the 15th November and will also be debited a full amount on the 30th November because my salary for December will be paid on the last day instead of the 15th since I’ll be changing employment. Where will I get money month end November as my last salary pay was 15 November?