[mothered]

And which reason should i choose for opening the dispute?
Further details: the object is 10 to 15 kg heavy and 65 cm long. It is an electronic device, so it has battery. The box will be kinda bulky i guess.

With PayPal Buyer Protection, there's two types of claims that can be made:

(1).  INR- Item Not Received, which Is similar to the DNA method.
(2).  SNAD- Significantly Not As Described,  just like the wrong Item received method.

Given the weight & dimensions of the Item, I'd say SNAD Is the better option.