NCO Financial Services

I have received several calls from this company to my cell phone since July, including left messages and one just less than 5 minutes ago. They are looking for a person with the name called "Alex Chong" (spelling?). I have told them that I do not know this person. They said that they will take out my cell phone number from their database. But until now I still receive their phone calls. When I asked to speak to their manager, they transferred me to a phone, whick kept ringning more than 10 minute and no one picked it up.