Unkept agreement

My name is MJ Serobanyane I have policies with this institution for a long time.I made clear to them that I am no longer getting my money on the 15th but on the last day of the month but today the 29th of the month they have deducted their premium unfortunately they took the money tha they were not supposed to take their's was comi6 on the last day of the month.They have messed up my plan.What am I supposed to do now because the money that they decided to deduct is supposed to go somewhere.