Why my request for friendship is not working?

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I requested for few users who responded to me so I requested them for friendship, when I clicked for this add as friend it changed to rquest pending, it was like that for few days and today when I checked my friends list I don't see these friends in my friends list and the request pending is again looking as add as friend like previous. Why it is like this? Can you help me how to add friends to our list?