Do I have an obligation to pay publication fee to predatory journal?
I am not a lawyer but I would think this depends on the contractual laws that govern you where you live and where the journal is based. You may be able to ask them to take down the article but they may try to do so through a retraction rather than simply "deleting" it. 

On the other hand, if you have not transferred copyright then they shouldn't technically be  able to publish the article, and you should still have had the right to withdraw the submission. 

So this is a bit of a thorny situation and I would try to seek out help from your university (do they have a Legal department in the administration?) to guide you through this process.