For minimizing SPAM calls, will using the supplied ATA be better than using SIP credentials on a BYOD?

I am in the process of porting two lines over from another VoIP provider, and I am getting a lot of SPAM on the first line with the old provider. I wanted to make sure my SPAM problem doesn't continue after the port is complete.

Some background: The caller ID shows up as three digit numbers. My first line at the old provider is set up with SIP credentials on UDP port 5060. As far as I could tell, it may be possible that bots have found me at that port number. I've changed the port number to see if that would help.