Blacklisting

I had a contract phone with Nashua Mobile and was using a MTN (simcard) network. Last year i terminated my contract with Nashua Mobile after rumours that are closing down all their retail stores. After ternimation of the contract the sim card was ported to Vodacom as i app**** for a new contract phone with them and wanted to keep the number. Unfortunately the contract was declined at Vodacom and the sim card was on vodacom prepaid. The phone now is ****** and need to be blacklisted for my insurance to pay back it up but vodacom neither MTN can not pick the IMEI number of the phone and they told them that only Nashau Mobile can do the blacklisting and they are no where to be fond. It really frustrating as no one can help in this regards. Went to Autopage but was no luck.