I have divided my 24c65 into 4 arrays of 2kB each
WHY, HOW, it is a simple memory, you have 16 address bits, it is straight forward what are you talking about.
I can read the data though, but it isn't the data I wrote to it.
are you reading the address you are trying to read as data?
So my guess is that I have to change something to my writecycle once the
adress is 1000h or above.
NO

Erik