I need urgent help my Betta fish cut his tail again !!!?

so i asked this a few months ago and your advice worked and he was healing really well !!! i removed the plants and put in Betta friendly plants ... i realized that he is cutting it again so now i put only one plant in hoping that he would heal that isn't the case ! he has one other ordinate to hide in he likes and sleeps in it but i think what might be the problem is the filter ! i noticed that when there was nothing in his tank he still cut his tail some how , but how could that be when he is in a betta tank and the filter came with it stating it wouldn't hurt his tail ? i seriously need help it is getting shorter by the days