My 3in1 packer seems unusable for penetration,help

months ago i bought an axolom giano stp (6.1in) with the flexit harness and the giano rod.
I wanted something that i could use for daily packing,stp and sex but i just can’t get the hang of it.
i tried many times to have penetrative sex with my girlfriend but the packer keeps slipping out in every position or ,even worse, yesterday it was kinda benting inside my gf’s vagina and it hurt even with a condom on.
I’m very lost,I think it’s the rod’s fault since it doesn’t make the packer super firm but maybe i just need to try and change positions/wearing it differently.
It’s both of us fist time so maybe i just need to be patient so If any of you could help with an advice I would be very grateful.
However if you could also recommend maybe another axolom rod compatible with the giano who makes it firmer it would be appreciated.