Monthly Harassment despite my account being in good order

My husband, who is the account holder, has made arrangements to pay our credit card account by the 30/31st of each month. Yet, every single month around the 19th, we start receiving calls asking when we will be making our payment. So, last month, we decided to pay the account early, in hopes of avoiding the calls - so this month, they started calling us on a SATURDAY, the 11th before 10am. Often, we take the calls, speak to an agent, explain that they can check the statement and see that we pay on time every month and that as always, we will pay by the 30th, just for a new agent to call us the very next day. If we miss their call on my husband's number, they will call mine and have even harassed my mother-in-law at her home number. No matter what we do, we can't seem to stop them from harassing us, despite our account being in good order. I am sure that they are also charging us for these calls.