Forget talking to anybody and try blocking the number. Telling them not to call you anymore is a language they don't understand and there's a slim chance they'll honor your request. If you can't block it, shut off the ringer, or any answering device and let the phone ring. They keep calling, disconnect the phone. They get nothing from numbers that have no answer of any kind and they'll give up eventually. Be patient. A call blocker may be of some help, but if you would rather not spend, completely ignore unknown calls in all ways.
Telemarketing - In some cases for their student at entirely. Now you can stop worrying about your student loan payments press one to see if you qualify for loan forgiveness
Called about student loan debt when pushed the number to see if I qualified they said there was an enrollment fee and I said I was not interested and they hung up.