Enable is the clocking signal for writing and reading. Normally E is low when nothing is accessing the display.
To write data or command, put the data byte on the port pins, then take E from low to high, and keep it high for 500 nS or longer. Then take E low again. The data is clocked into the display on the falling edge of E. Do not do another write until 1 uS has elapsed. That means you may have to use a delay while the E is high, and again after it goes low, to meet the timing minimums.
Do you need the explanation for reading?
This info is on pg 9 of the data sheet, and you are good at reading data sheets, right?
Seems like there is a problem in the negative voltage genertor circuit on the display. You should send an email to CFA support (see the "contact us" link at the top of the page), and maybe they can arrange for a warranty replacement. In the email, put a link to this thread, so they can see what has happened so far.