DH and I are homeowners and also have an investment property. We have been looking for a bigger home for a few years now and finally purchased one

We had preapproval from the bank for an extortionate amount of money and spent approximately half of this amount on our new house.
The bank has been a nightmare.
We provided all the documentation required very early on in the process. They came back and asked for additional info eg we provided payslips, group certs, rental statements, they came back and asked for the actual tax returns and more up to date rental statements (we gave them the most up to date ones we had at the time, which were the most recent ones). We provided them with the additional information they required and were assured that once this was done the loan would be unconditional.
They have come back today asking for even more information/documents!!!! I am getting so upset as I don't understand why this is soooo difficult when we are only borrowing half of what they offered us. Admittedly since pre-approval I have gone on family leave, but we were very upfront about that at the beginning.
Is this normal post GFC??? We are supposed to settle at the end of Jan and I am getting so stressed that we will lose our (very substantial) deposit. We told the broker today that we wanted to look at going with another lender and he has lodged a complaint with the bank on our behalf.
Anyone else had an experience like this? We are very fiscally responsible (not that the bank cares) so am struggling to understand why this is so hard