Question: Was there a series after the three episodes called 'The rebirth' called Transformers: Headmasters? Because I saw an old video of Transformers in a shop once called that, or is it just 'The rebirth' I saw?
Answer: There was a longer Japanese series called 'Headmasters' that ignored Rebirth and took it from there. However, The Rebirth was released on video in some markets as 'Headmasters'. Depending on where and when you saw the video, it's likely Rebirth.
Answer: The Headmasters series was in place of The Rebirth (ignoring its events) it was drawn by the same animation company but translated from Japanese scripts into English without any of the original voice actors returning to their roles, likely Japanese actors with good English and subsequently the translated scripts, and story lines, were terrible. Names didn't match up after translation (Blaster becomes "Billy", Blurr becomes known as "Wally", Jazz is "Marshall", Hot Rod is "Rodimus" (pronounced "Roadimus"), the Matrix becomes "the Power Pack", Spike is "Sparkle", Soundblaster is "New Soundwave", Metroplex is called "Philip", Cerebros is "Fortress", and Fortress Maximus is known as "Spaceship Bruce") So, the resulting series was barely watchable, I bought the whole box set myself several years ago and only ever sat through it once.