I had new siding and vents put in 2 years ago when I did an addition. Tonight I find that the dryer vent has come unattached from the outside and when trying to reattach it, I found that the tube that goes thru the wall had been cut off flush with the interior wall of the house and the dryer vent (which is soft flex) was riveted to it).
Of course, now, I have nothing to reattach to. I attached it temporarily with metal tape and will get replacement parts this weekend.
Do I need to replace the outside portion of the vent due to them cutting it off?
is there a good fix for this?
Any advice is very welcome as this was a surprise to me.
thanks in advance!

What reason would anyone have had to cut it off? Maybe it became short because the new siding added extra thickness to the wall. In any case, you should be using rigid metal duct for the dryer, and not flex, and it should be as short and direct as possible, with a minimum of bends.

No reason that I can think of. The wall is not that thick and there was siding on there before. The problem that I now have is that i need to attach something to the inside part of the wall to hold the vent in place so that the heat and moisture goes outside. I looked at possibly removing the vent and replacing but unfortunately, that would not be an easy task - not only is it nailed in place, it is also riveted. I can only believe that the riveting was to attach the flex dryer vent into place so that I would not notice their error.
Now I am stuck with this and can't really wait to long for a solution - laundry piles up and we were to get caught up since I had been unable to do much due to an injury.
I am replacing with a 90 degree elbow at the exit of the dryer then solid metal flex hose from there to up and out of the basement. Now I just need a coupling of some sort that I can screw to the interior portion of the wall to hold the hose in place. Hopefully our local stores will have just what I need.