there is no such as seven jannah, what people are confused about is when the seven heavens are mentioned in the Qur'an but also Allah mentions the seven earth at the same time therefore, the seven heavens are places where the Angels abide but not jannah where Allah Has created for His slaves they are two different creations that is why Allah have said comparing between the heavens and jannah in size, [Race toward forgiveness from your Lord and a Garden whose width is like the width of the heavens and earth, prepared for those who believed in Allah and His messengers. That is the bounty of Allah which He gives to whom He wills, and Allah is the possessor of great bounty] [57 v21] Allah here say, [Garden whose width is like the width of the heavens and earth] this means and proves jannah is not the heavens nor is it part of it, secondly there in no comparable between the two as Allah says just the width of jannah is the size of the seven heavens and earth, meaning it is bigger then both together.
It has hundreds of thousands of levels the level of those who are martyrs are one hundred levels to themselves between each level the distance between the heavens and earth and all these levels are for one person only.
What we also know is jannah has eight gates which the Muslims will enter trough for example there is a gate called [Ariyan] and it is the gate of those who fasted will enter and you also have the gate of [salah] and so forth so in total they are eight gates. To conclude jannah is not the seven heavens but it is different creation of Allah.