Seat Ibiza battery is always dying after a week or 4 days of not driving the car

You may have a parasitic drain , check it out . But you may have a battery with weak cells that wont hold a charge if so . Get battery LOAD tested

My battery is only 4 months old now, and the alternator works well too because when I am driving the car everyday it's perfect but when I went for 26days abroad, I came back to a fully dead car, even the remote control didn't work, I checked it before and I definitely see that something is still using the battery even when the car is off and locked, I wonder if it is the underseat LED lights because apparently someone who owned the car before me had them fitted, I am looking to take it to a car electrician this week, and hopefully we can get it sorted

" I wonder if it is the underseat LED lights " disconnect them and find out .

They weren't plugged in when I went abroad but they are connected to somewhere with the car electricity, I don't know alot about Mechanics and electricity, so I had it booked with a car electrician, fingers crossed hopefully we solve the problem, thank you so much for your time and replies