回複：要在規定的時間內(一般30天)回複討債公司

In the first letter, it didn't say that I have 30 days to reply. I did call them right after I recieved the letter but I didn't put it in writing. I realize that I have made a big mistake for not doing that timely.

The 2nd letter from the Debt Collection Agency came to me asking for $100 more interests in addtion to the bill.

Though I can send letter to dispute now, it is for sure over 30 days from the first letter that I received. Does it put me to a bad situation?