Your IPtables rules are in conflict. IPtables works on a first-match basis. Using the
-A option puts a rule at the end of the list so your
ACCEPT rule is at the end.
Thus if you entered your rules in the order you described your packet that matches that description (a tcp connection at port 2001) it will be dropped and will not concern itself with any of the following rules. That is of course if these are your only rules too!
I understand that this link is pretty old, however it provides excellent information on how IPtables priority of rules works.
So you will want to clear out that rule. First you need to identify the rule, then delete it.
sudo iptables -L --line-numbers
sudo iptables -D INPUT [The Number of the Drop Rule]
Next you can re-add the rule like you did before using the
-A option. Now your IPtables should work as expected.