Other features, terms, or problems: Credit card

I have been getting 10-15 calls per day, 7 days a week, for about two months now over a missed payment months ago. Payments have been scheduled since then. I have called them to cease harassment but every time they claim my call breaks up. Mind you, my balance is less than $100.00. They call from blocked numbers as well as from different area codes. Hundreds of calls from hundreds of numbers. This is illegal HARASSMENT