unlock sucsess but my phone relock !!

hello all
first I want to thank the developers made octoplus box it’s strong box !!
second : i used the box yestarday to unlock my s6 edge+ ( t-mobile Version ) it success but today the device shocked me when i try to use my sim and it’s lock again !! is this normal !! is there any solution for unlock that device for ever !!
sorry for my bad english