Just an update, yesterday i have received an email from SparkPost(from someone called Mitchell, their vp for global customer success), where they apologise for the way they have handled this whole situation, apparently they read the forum and saw that other customers have bad experience with them as well and they said they are committed to do better. They have also enabled my account.
At least now i can test the integration between mailwizz and sparkpost for other customers, in case there'll be issues, thing that was impossible with my account disabled.
Anyway, we're all grown-ups here so hopefully we can learn something from the above.