Not a teacher.
I think the first one is incorrect the second is correct.
Although I'd repthrased it to :
I regret to learn of the difficulties you experienced.
Experience is neutral if you regret something then I think you should indicate it wasn't pleasant.
I regret to learn of your unpleasant experience with .....
Be regreted is used in passive voice :
It is to be regretted that .....[ you have experienced such difficulties ]
I'm regretted means somebody feels regret for you for some reason.
You could say : I am so sorry about the difficulties you experienced.
Student or Learner