Daydreamyrhh , the best practice for a new Uke is to communicate with the seller/Dealer/Vendor whatever you want to call them, and to work reasonably, and with mutual respect, toward a resolution.
As you've had the instrument for some time it may or may not not be a fruitful outcome, nobody can say, however it is a perfectly normal thing to communicate with them , as you've done.
So, if the dealer is willing and able to rectify the problem, then Good, and if not , or if you choose to , then you can check and rectify things yourself, and it does often take a process and it may or may not be a process of elimination, regarding those factors already mentioned, again nobody can really say for certain at this time and under the circumstances.
Another thing to check is the Nut is actually properly placed, in other words straight, level, and perpendicular to the fretboard surface , it is a possibility that it may be inclined in a lean or an improper angle , other than most suggestions are covered in previous posts.
Checking your Nut does not need to be difficult, it does require care and patience, and a little bit of manual skill, which can be challenging at first, but not to fear, working on a saddle or nut should never be something to fear in this world, which is a rat race and a battle zone at times, and nuts and saddles will cause you no serious harm. I hope you find a resolution and can enjoy your ukulele.
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Happy Ukeing