NVC asks for payment before sending Welcome Letters, is it normal?

[glnofategl 0]

 

My NIW i140 was approved late July. Initially, it was not current because of my country of chargeability. Then it was made current by cross chargeability mid-September. Then NVC informed that they are ready to receive payment etc. 

However, I don't receive any welcome letters, so cannot log into the NVC website to proceed. 

I called and obtained the Invoice Number (apparently they have generated it not long after my case became current). But with the case ID and the Invoice number only brought me to a message "Please be advised that the case that you have attempted to access is not eligible for further processing by the National Visa Center at this time."

Surprisingly, a few weeks ago I received an automatic email sent by NVC asking for payment and form DS260, shown below.

"Good day,
The National Visa Center (NVC) received the documents you submitted in support of xxxxxx's immigrant visa petition. This petition's NVC case number is SYD2017xxxxxxx. However, NVC will not review these documents until we receive an Immigrant Visa Application (Form DS-260) for each intending immigrant. Form DS-260 must be completed and submitted to NVC online at ceac.state.gov. "

 

I really feel something has gone wrong with my petition. Any advice, please?  Thanks.