Telkom Mobile Cannot Blacklist a ****** Iphone

I phoned Telkom Mobile to blacklist my daughters IPhone 8 Plus after it was ******. She was using a telkom mobile sim card at the time of the theft and has been for the past year and a half in this specific phone. I received a message from Telkom mobile to say that I must contact Cell C because the IMEI number of the phone is registered with them. I phoned Cell C but they no longer have the pay as you go number active on their system from a year and a half ago. In the mean time I cannot blacklist a ****** phone and claim it from my insurance because Telkom, who was the last service provider on this phone for the past 18 months cannot assist!! Absolutely shocking service!!!