Lag is unbearable

This game is fun when it works. Bought originally when it came out but decided to sell it. Bought digitally when it was on sale and now I regret it. My first few weeks with digital copy were good but now the lag playing slayer is unbearable. Enemies glitching across screen, losing melee battles, shots just not registering and now people just appearing out of nowhere and killing me. I’m done.