As far as I know and if it wasn’t changed very very recently, Not paying the RPRF fee from the start is not grounds for a returned application. They ask you for it later in the process. Your rep is probably lying and messed up somewhere else. I suggest you remove them as your rep (there is a form for it) using webform and get all updates directly to you. If they messed up before the file even started processing imagine if they mess up or delay in giving you timely updates about biometrics and medicals etc.I got married in October 2018, submitted sponsorship application in Jan 2019. Got an email from my lawyer “CIC has asked us to pay the $150 dependent child sponsorship fee. With recent changes they also require that the right of permanent residence fee ($490) for outside sponsorship applications be paid in advance. Please let me know what credit card to use for this and I will send them the receipts.” I’m not sure if that’s the case or anything such happened. They said it’s not their fault as IRCC never updated about this change.
They never told me that application was sent back. When I literally yelled at them and told them that I have the right to know where my file is then she told me it was returned and they submitted again, which was received on April 26, 2019. What a waste of time!