saheli

Guys, I m going for PhD in Fall 2015. I had my fair share of admits and I had accepted the one that suited me. I was completely prepared for the university. But suddenly I got an opportunity from my dream institute with full funding. As it is April 15th passed, I am expectedly confused and worried about my next move. if I accept university B, then what should I inform University A? Will they accept my denial? Is there anyway they can actually stop me from a visa approval and getting into the other university? Actually I want to be honest with them and inform them as early as possible. But I am sceptical. what if they inform the visa office and see to it that I m not issued a visa to any other university. I have also resigned from my office. So it is important that I go this time. But I really want to accept University B. Please help. Thanks