bad adress after posting comment

My post adress is like https://mypage.com/here-is-my-post.

When someone adds a comment it takes him to the https://mypage.com/here-is-my-post//comment-page-1#comment-7995

there are 2 slashes before comment-page, and it shows a 404 error in stead of a post. i need only one /

how can i change it? which file is where is the line responsible for the adress after adding a comment?

thank alot