CPP-D with Wsib and LTIP

I am currently receiving WSIB benefits, but Manulife is now paying my pension. Manulife had me apply for CPP-D and I was approved. I received back pay to my date of injury. WSIB has confirmed with me that they will offset the amount I receive from the date I was approved for CPP-D but the rest which I received they do not take. Now Manulife has cut me off until I can provide them with documentation from WSIB (which I am waiting for) to show how they are reducing my payments. As WSIB is my primariy payor, can Manulife take the retro pay? Anyone else have a similar experience?