Blocked phone

<p>I bought my blackberry Z10 in 2013 at Nashua mobile Sunnypark branch in Pretoria and the salesman's name was Ismail,since I had the phone in 2013 I have returned it at least 3 times to the store as it had some problems..and the last time I returned it I was given a new blackberry Z10 but refurbished which I've been using from 2013 to date,now recently I've recovered that I can't make nor receive calls from this device as it gives me an error message "MM#6"which means according to my research that the device has been reported ****** or blocked with the IMEI no.All I have right now is the device and their monthly statements as it was a contract phone ..I don't have the box or any other proof that I bought the phone because it was like 4 years ago,however I believe Nashua mobile still has my records that I bought this device from them and these statements should be sufficient.Now I have no idea what to do with my device because it's blocked and I thought I owed it.Please help Peter..</p>