As per the user manual for this model, the joystick control can not access the setup menu.
Is the remote control the usual infra red type?
If so, you could double check your remote is actually working using mobile phone camera.
You might find that any Panasonic TV remote control could be "mostly" compatible with other/your Panasonic TV.
So if you, or neighbour, friend, family member has one (or a Universal or programmable remote) you could try it and likely to get TV to turn on or access menu.
Assuming the receiver on the TV itself is not faulty.
If TV is only 4 months old it should be covered under warranty.
Alternatively, you may be able to use a Panasonic TV remote control app on mobile phone.
Hope you can sort out the problem soon.
Strangely, my remote stopped working today as well. Mine was just unresponsive all of a sudden. I looked online, and the solution I found was to take the batteries out, hold down the power button on the remote for over a minute, then push lots of remote, just loads of them one after another for a while, and then put the batteries back in. It sounds crazy and simple, and I was sure it wouldn't work, but it did. I think the 'science' behind it involves depleting it of charge, so it can reset itself. Try that! Its worth a shot.