new playerFrozen[MAX_PLAYERS];
TogglePlayerControllableEx(playerid, status) {
    playerFrozen[playerid] = status==1?0:1;
    TogglePlayerControllable(playerid, status);
}
isFrozen(playerid) {
    return playerFrozen[playerid];
}

//Usage:
TogglePlayerControllableEx(playerid, 0); //to freeze them and 1 to unfreeze them

if(isFrozen(playerid)) {
    SendClientMessage(playerid, COLOR_WHITE, "The player is frozen");
    return 1;
}