I2C - Where's the ACK
With the scope,  you should see some sort of effect on the data line, even if the line is being pulled up too strongly.  It may drop only half a volt or something, not enough to be read as a zero.

There's also the possibility of the slave address being wrong.  Sometimes the address is specified as 7-bit and sometimes as 8-bit. The latter will be 2x the former.  Free advice: Write a loop to try all the addresses and stop if it finds one that responds.