HELP! IRS 2018 Tax for crypto

Hi a few days ago I received an IRS letter says that I owe $1744 for trading crypto coins but I didn’t even trade that amount, I did a total of 65 times small little trade and I ended up with a loss. I don’t know what should I do now and unfortunately, I file the tax with the army free tax help center that year… I only got $100 back… I wonder what should I do next? I couldn’t upload the excel into Koinly…