Read here: Flash K800 CID53 with K810 software CID53 (for begginers), but use these files:
1. K800_R1KG001_MAIN_GENERIC_WI_RED53 (Downloads > Firmware > K800 > RED53 > R1KG001_RED53)
2. K800_R8BF003_FS_EUROPE_4_RED53 (Downloads > Firmware > K800 > RED53 > R8BF003_RED53)
3. HB1-06_Gen_CDA102568_13_R8A_GENERIC_EUROPE_4 (Downloads > Custom Files > k800custpack)
After flashing you can Full unlock phone forever with Omnius