Unprocessed debit

I changed my debit date to the 15th of every month from the 1st of each month. I was advised that I will have to pay a pro-rata which will be debited within 48 hrs of calling (I called on the 15th). The debit never happened, I called again to inquire what could be the problem, and was then advised that the debit will take place at the end of the month (month of April), which never happened. I had budget this for the month of April, and Discovery didn't fulfill their agreement. I called again today to find out what could the problem be, only to be told that the pro-rata was never processed and will be debit it in combination with my monthly payment. I am not impressed nor happy with this because I was told three different things, and now I might be inconvenienced as the pro-rata is not in my budget. Not happy at all!!!!