This is the lamest and lousy replacement policy from a so-called telecom giant. They won't give you any document regarding your replacement request!
I would suggest you go back to that store and demand a replacement receipt indicating such request, date of request, initial unit diagnosis and approval of said request. Puputi ang uwak nyan pag hindi ka nagrequest ng receipt. Baka lalabas na ang iPhone 6s hindi pa napapalitan unit mo.
Request that your plan be suspended until a replacement unit is handed to you. 7 day replacement is very clear that they will replace it immediately!
Nakakagalit ang ganitong sistema.