Interest, Delayed Response

Hello, a few things:1. There were 2 questions where I asked a follow-up, one of them was a very long time ago and you still haven't answered me.2. There was a time when I told you about a situation (the bus fare was then 5.5 and then it went up to 6, and my friend paid for me when it was 5.5 and I told him mistakenly that it was 6.So you told me that inorder to avoid the issue of interest ריבית , he should return 20 agorot to me), The problem is that I have already reminded him many times and he does not return it (maybe because he forgets or for him it's just 20 agorot so he doesn't pay attention), am I exempt from this and he doesn't need to return it to me, how many times can I remind him?! (Of course, I mean 'exempt'  -so that I don't have any issue of interest)

Shalom Rav, 

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You are not obligated to 'nag' him. And you are allowed to forgive him.