I bought a phone from a certain mobile phone network for full price, under no contract and used a prepaid plan for about six months before trying to change my service provider only to find that my previous provider had placed a lock on my phone. This disables me from using my phone with any other providers. After several attempts to contact someone in their costumer service department who even knew what I was talking about, someone claiming to be a manager said they could not and would not unlock my phone. Do I have a case?