There are a few I2C scanner sketches floating around. They scan the I2C bus for active addresses and report the results via the serial monitor.
It would be worthwhile to try this to verify that the I2C address you think the display is using actually
aligns with the one that the display is really using. That will at least eliminate that variable from the equation or perhaps fix your issue if
there is a mismatch.
P.S. The Scanner sketch that I use can be found at :