The law on rights is now 2 years when companies can dismiss without cause, however notice has to be paid
Dismissal without notice is usually only in the case of gross misconduct, and that would require the full implementation of the disciplinary procedure (i.e - investigation, disciplinary meeting with due notice and the right of accompaniment, and an appeal procedure). It sounds like this was not followed in this case
Failure to follow this would usually mean that one could sue for wrongful dismissal at least, but the basic award would only be notice, but there is a cost of issuing proceedings. At best, unfair dismissal might be claimed, but harder to make stick.
Therefore, the best course of action is the internal procedure