Creeping buttercup infestation

Hi folks, trying to get a portion of our forrest garden tidy and our whole site of 2 acres has become overrun with creeping buttercup. We had cleared everything and planted ‘special forrest grass seed’ that died completely after one season. Any suggestions would be great. Do a mow it all down to the ground or higher and re seed with grass and let them battle it out? Thares nice stuff doing well that I’d like to i courage but the creeper is so aggressive it’s overpowering everything else. Thanks in advance Mike