I don't understand why but my account was banned just for the reason of low post value
Not enough reason, you think? Do you intentionally make low quality post?
I am not really the first owner but I am currently the last owner, you can look at the history up to now, a very long time attached to this forum. I have been participating since the time without merit until now, and we cannot use merit to evaluate a post quality.
Why buy account when you can easily create one by yourself? It is very easy to create account and that's what you would have done if you had the ardor to share your knowledge here and not just having the ardor to join signature campaign. It is not a logical attitude to buy account just for participating in signature campaign, you would have known better if only you had registered a new account and contributed with quality post.
Merit might not be used to evaluate the quality of a post but if you make quality post or comment in a thread and the OP appreciate your helpful feedback, they will merit your post and when a merit source also finds the post helpful, they will still merit your post, that means that merit is use to determine if the post was not just quality but very helpful.