I am not familiar with limit topic as of yet so I can't tell whether the first is a duplicate of second but I can tell you what to do.
But I can tell you what to do if you arrive at a question closed of duplicate which should not had been closed-
Cast a reopen vote
If you have reputation $\geq 3000$ then besides the edit button there would be a "reopen" button. Just click on that and it will come in Reopen queue and if some number of people also wished to reopen the post the post will be reopened.
In some cases, a single vote is enough to reopen the question:
A single vote from a moderator can reopen any question closed for any reason immediately.
Questions closed as duplicates can be immediately reopened by a user with a gold tag badge for any of the question's tags.
Try commenting on the post
Just to repeat user1729's comments:
Commenting has two advantages: firstly, people interested in the question will see the discussion, and secondly if it enters the "reopen" queue then voters will see the discussion (and so have to think less)
Edit the post
If the comments are helpful as to why the question has been closed, you can edit the post so that it's a good, on-topic question, or to explain why it's not a duplicate. The close reason, while not always accurate, should point you in the right direction of what to fix. If your edit made others feel it should not had been closed as duplicate it will be reopen
Bring forward the issue in CURED chat room
You can bring forward the issue at chatroom CURED. Just paste the question there and write like
Please unclose this question [link]. This was closed as duplicate but it should not had been closed.
Also if you are not 100% sure whether it should be unclosed just use ask anyone in the room. You can definitely talk to many over there as many of them have enough experience of closing, reopening, deletion or undeletion of question. Some questions are closed/deleted/unclosed/undeleted with help of cured room only but not all. Can't wait to see you there.
Request for reopening of post in reopen post link
If you want to reopen/undelete a post just write a answer over here in the same way others did writing the question and then explaining the reason for reopen and undeletion.
Request on meta to reopen
This one should be used when all three above methods have failed. You can request on meta to reopen a post and tag it with support reopen-request.
To get more help with reopening post you can visit this