Repeated Problems w Internet Service and Need a Way to Disable SIP ALG

Hi,

I've tried speaking with the non-technical, tech support team many times to no avail. My Internet w ATT has had non-stop repeated problems. Recently, I called ATT to request a new router that would allow me to disable the SIP ALG (which is rejecting packets and causing problems). The one they had given me blocked users from doing that. I do not want to change the DMZ as THAT is what truly opens someone up to vulnerabilities, and not disabling SIP ALG. I won't even go into the circus I've run into of people making up answers each time I call in. I was ASSURED I would be given a router that allowed disabling of SIP ALG. The tech guy that came out was knowledgeable and great about other stuff, but not familiar w these types of router settings. 

I considered getting ATT Fiber, but again, no one will tell me the hardware prior so I can ensure it allows disabling SIP ALG. The new router is WORTHLESS and of course, does NOT allow it, although the rep PROMISED me it would. There is NO ONE I can reach at ATT who knows even the SLIGHTEST bit about basic technology. The last guy put me on hold for 30 minutes finally to come back and read me the definition of SIP ALG that he had finally found after searching 30 minutes. 

Is there a router I can request that will allow me to disable SIP ALG? Is there a way I can disable SIP ALG if I get the ATT Fiber?

Thank you.