How do I fix my vanity unit?

Why is there such a large gap? Does the vanity top stick out behind the vanity? Is it because of the plumbing? Either way, whoever installed it should have discussed solutions with you and not just left it that way. Call them back. If you could post a picture, it would be easier to see just what the issue is. Without doing a lot of work, you could apply a complimentary wood trim to cover the gap that would fit under the vanity overhang.

And you paid them??? Uh, not acceptable. Call them back to do the job correctly. You don't owe them any more money. It's on their dime. Don't let them give you a song and dance. Go to a kitchen and bath showroom or poke around on remodeling sites to see how it is to be finished off properly. If they don't comply, go after their license. Do you have a signed contract?

Call whoever you paid to do this and tell them this isn't acceptable and ask how they would like to fix this?

If you can't get the workman to fix it, I think applying a piece of molding along the gap might work.

Did you pay for a backsplash to be installed as well? (first picture below)

Is there still a baseboard between the wall and the floor at the back of the vanity cabinet? Removing it will allow the cabinet to be moved a little farther back, although 2 inches is more than 'a little'.

Also, I am wondering if the plumber (or whoever installed the sink portion of the vanity) measured correctly as to the distance from the drain hole connecting with the pipes coming out of the wall? The depth away from the wall to the drain hole varies with different sinks.

It can be done, but to accommodate the new sink, the elbows in the drain trap may need to be reconfigured. (second picture below).

There is no reason there should be any gap. They should return and correct the problem. The drain pipes are adjustable to fit any sink if that was a reason. If there is baseboard it can be cut and removed to allow the vanity to be against the wall.

I would call them back to fix it. If they won't, a piece of molding may be your answer.

Another vote for having them come back and fix it. This job wasn't finished.

Trim is the best way to cover gaps but I am shocked that a 2" gap was left. I would contact them to fix it.

You paid to have this done now ask them how they intend to fix this problem.

Hi Maria, you can tidy that gap up with some trim, nowadays you can buy peel and stick, this helps you get the job done with a measuring tape and a pair of scissors, here's link to one place that sells it, it may be at the dollar stores too

https://www.homedepot.com/b/Building-Materials-Moulding-Millwork-Moulding/Peel-Stick/N-5yc1vZara1Z1z11crp

That is unacceptable, there should not be a gap. Call the contractor and have him fix it. If they will not you can purchase a stove spacer on amazon, they come in white and black and will fill the spot.

Honestly, have him come back and fix it properly.