Credit card dispute with United Invest International

I purchased a equipment from United Invest International on July 20, 1981. Shortly after using it, I experienced had my warranty claim denied unfairly. I contacted their customer service on multiple occasions, but they have not resolved the issue. I spoke with Humberto S. who promised to escalate my case, but I've heard nothing since.

I purchased a equipment from United Invest International on July 20, 1981. Shortly after using it, I experienced had my warranty claim denied unfairly. I contacted their customer service on multiple occasions, but they have not resolved the issue. I spoke with Humberto S. who promised to escalate my case, but I've heard nothing since.