Need advice on job

Hi

I have 6 years experience. I am in bench right now. I am in service based company . I have attended the interview for another service based company . But they have asked to attend 2 virtual rounds . Then they asked to come for managerial round . There also I have attended 2 technical rounds again and then one HR round . She told whatever certification it is, we can't provide not more than 50% percent hike. I have accepted it. Now again she is asking me to attend another HR round . I confirmed that if they provide me offer letter I can get relieved in 1 week . But they are asking me mail confirmation from my HR . Already confirmed with my HR verbally. I an asking for mail confirmation from them but they are keep on delaying it. Now they are asking to join immediately and their behavior is so rude to me .I don't need any offer letter or nothing. I need email confirmation from them . But they are not giving me that. Asking me to attend interview again and again.