Multiple journal submissions I was a junior researcher and I submitted a paper to journal A. After not having any response from journal A, I submitted my paper to journal B. After some months, journal A mailed me to say that my paper was accepted. 

I immediately replied to journal A saying that I wanted to withdraw my paper. They reverted within minutes that they have already published and paid x money for publishing. I insisted that I wanted to withdraw and they mailed me to pay y amount of money for withdrawal, which I paid. Then they mailed me saying that my withdrawal is complete. I have not signed any copyright form with journal A. 

After a few days journal B published my paper. Now after one year, I see my name in a retraction list citing that journal A has retracted my paper due to “author’s personal concerns.”

How this can affect my career? I withdrew my paper, so how can journal A publish it without a copyright form? On the same day that they mailed me to say that my paper had been accepted, I reverted and wanted to withdraw. Can they publish it and then retarct it? What could be the consequences on me?
Within minutes they replied that they have already published, requesting me to pay x money for the publication fee. 


This sounds like Journal A was a predatory publication (i.e., a scam without real peer review), and not actually a reputed journal.  If this is indeed the case, then having a publication withdrawn from them may actually be better for your reputation than actually having published with them.

That said, you shouldn't submit to a second journal until you've already withdrawn from the first.  In the future, follow that procedure and also make sure that you're actually dealing with a reputed journal before you submit!