MBD Have No Work Ethic or Organization

After making an arrangement in January 2021 I have received to date a minimum of 3 to 4 calls a day, including a Saturday and once on a Sunday saying I have not paid, when I have.

Have just spent 10 min on the phone doing another arrangement because it wasn't done on January. Asked for confirmation of this and was told that it can't be done.

Am fully aware of my debt, and have been paying on a regular basis. Everyone else sends me a sms saying thank you for the payment, not MBD.

Am now being threatened with additional charges and fees. Right now I feel like paying everyone else except them. At my age why would I want credit?