Advice please: controlling a transistorised relay board with anopen collector output

Hi, I'm not up with modern electronics & I'm struggling a bit with this: if anyone can give me any advice or suggestions I'd be grateful

I have a device with an open collector output which can be controlled ON/OFF remotely by phone. I'm told I have to be careful about the amount of current supplied by the open collector output so I chose to use the open collector output to switch a relay with a transistorized relay board to trigger its relay.

I've got a 1.5k resistor between 12V on the device & its open collector output, the output then goes to the trigger on a relay board. When the output is ON theres 10.5V on the trigger, & when its OFF theres 0.7V on the trigger

Powering up the device has the open collector output ON & the relay is triggered ON, BUT, when I command the Open collector OFF the trigger voltage only drops to 0.7V, & the relay stays ON So I haven't got control of the relay as I wanted because I cant turn it off!

I've experimented & found I have to get the trigger voltage down to about

So heres the question, how can I get the open collector output down to 0.1V or if I can't is there a work around

TIA Frank Frank Sweeting

snipped-for-privacy@sweetingfam.freeserve.co.uk