If you have UCI and/or file/case number, you can upload the receipt via Case Specific Inquiry, and explain what you are doing.
It'll get to the VO.
In fact, your receipt is in PDF format...you don't even need to print it out and scan it again...just save the PDF file, then upload it into the system. In a sense, that's really the original.
When we applied, we paid everything upfront, printed the receipt and put it into the application package...then CIC sorted everything out.
In your case, if you only paid the application fee but not the second part (PR fee), the VO will send you instructions...not sure how that works, but I would imagine you email it or alternatively I am sure Case Specific Inquiry upload would also be fine.