I signed for a 150M internet a few days ago and recived my modem today
The modem I got is very old / refubreshed CGN3AMF
Is it possibe to ask to replace it with a new modem ?
Modems don't usally "die" unless they were physically mishandled and have physical damage internally. I just received an older modem as well with my 150/15 internet and it works fine. I have gotten used modems with prior providers and never really had any issues. Having said that, I'd recommend using a separate router for your wireless connections as built-in wi-fi isn't very robust for anything larger than a condo.
It doesn't matter if the modem is new or refurbished as long as it does its job, if it is not functioning then you can certainly have it replaced whether you get a new or another refurbished one all depends on stock.
I'm just afraid that the chances that so old modem will "die" are much higher compared to a new modem and I don't want to stuck without an internet or spend hours with tech support