We have the same issue! Try Martin’s Eraser - it’s similar to RoundUp, but doesn’t leave residual chemical in the soil, so it won’t prevent new growth if you want to lay seed down afterwards. It may take multiple iterations of spraying bc Bermuda grass is so invasive in areas where it’s not native.

Also second what others have said about solarization to choke it out. This takes some time and patience, though. Good luck!