Modem relocation - Alarm Co. phone signal conflict.

Recently moved in with Parents.  Poor signal in areas of any distance from modem/router which is located in furthest 1st floor corner under massive custom built in desk on firewall between home and attached garage (pretty much ticks the box of every DONT when determining equipment placement I know).  Moved it to centrally located office on second floor and signal was great in every location Crisis averted/Parents think I'm Genius!  Until...  2 days later home alarm system started sounding off every 15 min.  apparently to notify us that it was no longer receiving a signal from our equipment.

I guess it receives it thru a dedicated (might not be correct term here) phone line that comes into house in that 1st floor office and goes directly into the modem.  I really cannot run that phone line all the way up to the 2nd floor office I wanted to move equipment to.  I have tried repeaters, extenders, routers WAP's, etc. and nothing comes close to achieving the signal strength I get when Modem and Router is placed in 2nd floor office location.

I know this is the most annoying question on here so please do not hate me I did attempt to find a solution in these forums for quite sometime before deciding to post.  So my apologies in advance if I missed a glaring answer.

I have a duplicate model of my modem.  Could I possibly set it up and configure it to match existing exactly without paying for a second service.  If not I am open to any other suggestions.

Thank you in advance for your time.....