[Rdx]

Okay. Now tell me why there is a "!" character.
Try to remove it here:

if(!IsSATaxi(GetPlayerVehicleID(playerid)) && !IsSATaxiL(GetPlayerVehicleID(playerid)))

=

if(IsSATaxi(GetPlayerVehicleID(playerid)) && IsSATaxiL(GetPlayerVehicleID(playerid)))

You should remove it here too:

if(!IsTaxiDriver(playerid))

=

if(IsTaxiDriver(playerid))