Harassment from Edcon

I have an Edgars account. I receive numerous emails calls and sms from the call centre informing me that my account is in arrears. However my accoubt is paid on a monthly basis on a date that ive instructed the call centre agents to change on multiple occasions. I receive these calls because payment isnt made on the 1st of each month but on the 25th. Ive communicate telephonically and via email correspondence to change the date. I find these constant calls bordering on harassment as the account is paid monthly without fail. Instead of pestering me why not divert the energy to clients who don't pay at all.