Shadowfax courier - Package not delivered to customer or back to seller

I run Print on Demand Business & had ordered *tshirts for customer on print on demand & had selected shadowfax as courier partner, the order was dispatched but then i received message from customer that they haven't received any call from delivery person or Shadowfax Team, i contacted to deliver person multiple times but the number was showing unreachable/switched off everytime then i tried to reach on shadowfax Team on number given in shadowfax website but that number was also unreachable even after calling multiple times & days. They never called customer for address guidance nor they tried to attempt delivery on customer address, they just marked it as customer unreachable whereas delivery person was unreachable, then order was marked as RTO after * Wrong delivery attempts by Shadowfax.okay, After waiting for few weeks they marked the package as RTO delivered, I reached out to my print on demand manufacturer (seller) , they said never received any package of customer's name or Shadowfax, they requested me to reach out to Shadowfax for RTO delivered signed acknowledgement of them receiving the package as the POD seller sign acknowledgement before receiving RTO order. I reached out to Shadowfax Team multiple times through that same unreachable number, Email & Twitter regarding RTO delivered signed acknowledgement but they never responded or never sent me the acknowledgement. They Lost they package & marked it as Wrong RTO delivered Tag & aren't sending me acknowledgement if they really delivered the package to the seller. Package Tracking ID- SF**********KR