Change debit Date without authorisation

Direct axis decided to change my dabit date for December, I called and told them to please keep it as the normal date cause I don't get paid early which the consultant said she would do. 15 December they debit without my authorisation n it was rejected as I had not enuf funds. They didn't do the debit on the 25 as normal now I get calls from collections as if I didn't pay them when they have failed to debit my account on the agreed upon date. Such pathetic service