You may have to change ISPs. It would depend if the packet loss is on "your" side or "their" side. If you setup a ping to your router and get no packet loss, there isn't much else you can do.
The things you can change on your end.
- Use wired connection to your primary router.
- Put new cabling from your modem to the outside of your house
- Use new cabling between your PC, router, and modem
- Ensure your PC exceeds the minimum specs for the job and that there are no background tasks interfering.
- Contact your current ISP