Safe Home Security review: Home security

This was a security system I had won from a drawing at the mall. They called; they came over. They told me I won the system but no the service to make it operate. I wanted them to leave, after lots of unwanted conversation, we had agreed to a smaller length in contract and around $45. a month for 18 months. I get a call 2 years later stating I owe the thousands of dollars for a service that apparently, I didn't even know I still have. I told the guy on the phone that my contract was up at 18 months and have paid them every month. He began yelling at me. I hung up. About a month ago I find my credit score had dipped down almost 100 points due to this company claiming I still owe them money, and they have been still charging me for this. This is absurd to do business this way.