i was selected for their client project before 1 month but still now am not getting offer letter and if i call them they are not responding i lost my opportunity because of this consultancy.and they said immediate joining its already 1 month completed but no response from them

i got a call from the hr for the interview then i went for the interview and i selected for their client project after that salary discussions also completed.. the hr told me that the immediate joining i said ok but its already 1 month completed till now am not getting offer letter and am calling so many times to know about my offer letter but they are not responding to my call..