I failed my driving test second time

I had 1 serious fault, basically everything went well but the satnav said turn left then left again so I got to the end of the junction and it said turn left so I put my indicator on again after the turn and it was a no entry so I pulled back from my decision and kept going forward. I did mention to the driving instructor the satnav delayed and told me to turn left and he said he was just doing his job, He did have to interfere by saying dont go in there but I had already noticed and responded to it and got a serious for response to road signs.