Seja
Dont worry, it is normal to get your final approval 1 week prior to joining and then your accomodation details about 5 days prior and your ticket / visa around 2 days prior. I know its all very last minute but it will come :-). One thing you can do is send a e-mail on the portal explaining you would like acknowledgement of your resignation letter and to recieve final approval before your give notice to your current position, thats what i did and they replied with in 2 days with my final approval !