After applied to a phd offer in a cluster group in Germany. I've had a promising phone chat with one professor of the group. Our research interests are closely related and he told me i will receive a mail from the administration not from him. The interview went well, he was even querying about the visa procedure. But it's almost 20 days now and i did not received anything. I'm confused. Should i contact him to ask? And what to write? As he as warned me that the administration always took too much time. And i do not have any contact with the administration since the beginning.