Failing to blacklist

Good day I'm coming here for help I'm out of options I lost my device on the 16th of January I've been trying to blacklist it ever since so that I can claim. Have so many reference numbers they say they escalating the matter call back after 48hrs I call back I get a new ref call ref it's Bern ongoing and I'm frustrated now. May you kindly help me blacklist my device current ref number *** I'm trying to blacklist LG g6