they asked you to pay for the visa and there was no formal interview; i suspect you already know the answer to your question; they're scammers, there's no job and you will not send them any money; and most importantly, if i were you; i'd do my best to report this to the real DOPET and anyone else you can find in Qatar or on linkedin or whatever. Good you decided to get opinions here; i can easily imagine a more desperate or naive person falling for the trap and being fleeced of his money; may such scammers who prey on unsuspecting people burn in hell ameen...