Unable to Delete Network Interfaces

I am unable to delete two network interfaces (which cascade my inability to delete associated Subnets and VPCs):

• eni-034e9a42b5c8a5f5b
• eni-0c6c5569a0cebf4cd
  When I try to delete these, I get the error "The network interfaces can't be deleted." Reason: "Network interface is currently in use."

It seems that there are several posts on the forum with the same issue, and seems that it takes someone from AWS to address. Could someone assist me please? Thank you.