******** lapse of my Law On Call Policy

I got an sms that my law on call policy lapsed. A deduction was made on the 25th, I then got an sms that the next one including an outstanding premium would be deducted the following month. I then called FNB to arrange that my debit order changes to the 31st on the next deduction, which should be end of April. Lo and behold, FNB did not find the funds when they tried to debit my account on 31 March, because the agreement was for the deduction to take place in the next month (End of April). I cannot be debited twice in one month on separate occasion, so please rectify this mistake and re-instate my policy.