Cold Calls

The call Centre keeps calling me in regards to some outstanding balance they claim I have. As soon as I answer the phone the person put the phone down. I have tried calling back to find out whats going on but when I eventually get through to an actual person the phone is once again dropped in my ear and this has happen on more than one occasion. They call me like clockwork everyday, sometimes when I'm at work and can't answer otherwise when they call I answer and they don't speak. It becoming annoying and starting to feel a lot like harrasment