It definitely appears to be an issue with the 2.4GHz band setup on that router since you can access the internet with ethernet.
You mentioned that you have a Windows 10 PC that has no issues on that same router - which SSID are you connecting to on that PC, the 2.4GHz one or the 5GHZ one?
Using the Windows 10 PC try connecting to the same SSID as the Windows 7 PC. It should give you the same problem (LAN access, no internet). If this is the case there isn't much you can do since as you indicated your ISP wasn't helpful.
There isn't much you can do with this router unfortunately as it is what your ISP supplies.
TG2492 Touchstone TG2492 Telephony Gateway User Manual User Guide ARRIS Group, .
My ISP also supplies me with some All-in-one router/gateway with few options I can control. I have my own AC2700 router that I plug into their router's ethernet port so I have full control of my WIFI and LAN. This means I have no problems connecting to the internet wirelessly from any device regardless of band. Android, Windows 7, 10 even Linux. I have Windows XP on an ancient Compaq V2000 laptop with 802.11g WIFI that connects to the internet on this same router with no issues. I also have my Wireless printer and DLNA server on static IP addresses. Never had to call my ISP with WIFI issues because I'm the LAN admin.
You have 3 choices:
1) Find a compatible replacement WIFI card for your Windows 7 laptop.
2) Easier route would be as USB dual-band 802.11ac WIFI adapter (I purchased one for an older Thinkpad so I could connect to 5GHz WIFI.)
3) Buy your own router (optimal choice). Dual-band AC1900 routers are affordable and have more features than any ISP provided kit. No more waiting in queue for some unhelpful ISP tech who just reads prepared scripts to every caller. You will have full control of your WIFI and LAN and practically all new routers allow configuration/control from web browser or even mobile phone apps.
In this day and age where everything connects to WIFI purchasing your own router only makes sense and will simplify troubleshooting connectivity issues.
