Debit account 1 week before due date

1Life and myself contractually agreed that my account will be debited on the 20th of every month. Last month they debited my account on the 19th and unfortunately there was not sufficient funds to service the debit orders (BECAUSE I DO NOT EXPECT DEBIT ORDERS ON THE 19th !). The debit orders for my 2 policies were returned as unpaid and the bank penalised me. On the 15th, out of the blue the debited my account twice, even though October debit orders are only due on the 20th October 2015. Sent email at 07:48 this morning, contacted the call centre on *** twice, but they could not assist or give me names. I budgeted for this money for important things and 1Life just decided to take it from my account. I have been with them for years and if they submitted the debit orders on the 20th September, as per agreement/contract, none of this would have happened. i thought they were the best but they have just proven me so wrong. I am really very annoyed and frustrated.