Terrible service

So I have a personal loan and my credit agreement says pay date 20th of every month. Why would you collect on any other day unless the 20th is on a weekend or public holiday. Then you call their call centre and when you ask the agent their response is "that's a good question. Then you go into the bank they tell you no one has access to changing the date. Is this not a breach of a contractual agreement? All I can say is I will be closing this damn account because it is bull**** and no one can explain the **** to you. Like do your damn job know your ****. Call centre agents damn rude too. Edit