Sending PUBX commands to GPS Board (Ublox NEO-6M) through SoftwareSerial
I've tried your code sending those PUBX commands to a ublox module and they work successfully for me.

There are a lot of fakes about on the internet using AT6558 chips repackaged as ublox. Check the GPTXT messages that are output when the GPS module is powered up to see if its really a ublox module or a fake one like this:

$GPTXT,01,01,02,MA=CASIC*27
$GPTXT,01,01,02,HW=ATGM332D,0080113573899*18
$GPTXT,01,01,02,IC=AT6558-5N-31-0C500000,J7M911C-B2-008827*50
$GPTXT,01,01,02,SW=URANUS4,V4.3.0.5*18