Poor service / Not able to get a representative of the company to take any action

I've received various telephone calls and text messages referring to my X-husband's outstanding debt. I've been separated and divorced for over 10 years and was not a relative of him when he app**** for this debt. They are keeping on to phone me about 3 times a day and keep on sending me text messages even though I gave them the person's personal telephone number. I want to talk to the relevant representative of the case from the company, but cannot get hold of anybody that actions my requests. The outstanding debt will never be recovered if they just keep on phoning me and the actual person in debt is not made accountable.