If you have a new question, you have to ask a new question. Link to the other post as well so that the context of your issue is clear. If you can't ask questions anymore, you will have to work on having that ban removed, sorry.
I don't see how adding a comment to the answer would help you (or others) in the long run. If you have an issue, the fastest way to get it solved is by asking a question.
If you really want to add a comment, you have to wait until you have 50 reputation, then you can do so. There's no working around that restriction, really. Moderators can convert answers to comments, but this should be used in special cases, and not to help users work around their missing privilege.