Incorrect Debit order dates

I had it with Standard banks pathetic service. I have a home loan with them for more than 5 years. since the first time my debit order went off it was agreed that my payment date is the 27th of each month. Ever since December Standard bank has decided to make the date the 15th which no one has communicated with me. Why can this bank do and make as if they want to. Today was the last straw when i checked my statement that they wanted to do it again on the 15th they don't care whether you have budgeted for something else or have other commitment as long as they do and please with your funds like they want. I think its time i move my homeloan to FNB as i moved my cheque account and savings.