Cell phone contract dispute

I have a big problem with Ismart,this people they are not professional they lack good customer service.Each and everyday they are harassing me with their calls and I told them to remove my name from their data base.I had a contract with them 2015 I took a tablet the tablet only worked for 2 months and I reported it they took it back for repairs after 2 months they told me the tablet can't be repaired it is unrepairable,they promised me if I keep on paying the account they will replace me with another phone but they failed to do so and I was busy paying them for something I don't have.Now they put me through their attorney's by the name of Norman Bisset and credit worx their agents are harassing me each and everyday for something I don't have.Their agents are so disrespectful and rude to a point that when you are talking and explaining your matter to them they hang up their phone.I am so fed up with this people.