How to Change Corporate Travel Agent Issued Ticket Return Date

I have a SQ Business ETicket BNE - SIN and SIN - BNE issued by a corporate travel agency. 

I wish to change the return date without dealing with the issuing corporate travel agency - for reasons unrelated to the agent. 

I rang SQ and they stated I have to deal with the issuing travel agent-  against my wishes. 

Is there some mechanism I can use to change my return flight without involving the issuing agent? 

Cheers 

Yeah that's usually the case in my experience - have tried it a few times with business travel but because it's issued through agency - the airlines just will not deal with you :(

Sometimes the airline will take control of the ticket about 24 hours before departure of the first flight on the itinerary, at which point you can usually ask the airline to make any changes as needed - but there are no guarantees, of course!

(It's also why you can't upgrade on BA with cash until close before departure if your flight was booked via a travel agent, as BA technically can't 'change' the fare.)

I've had to do this once before. It was after hours and I had to change my flight for one that same evening. In that case SQ was happy to oblige as I had no other option. 

The agent 'owns' the booking - that way they ensure they get commissions and any change fees etc.
As above, once the ticket starts (possibly once checkin opens) the airline might be able to do more

The agent is paid commission to not only book the ticket but manage the customer. If the clients use the airlines resources then why bother paying commission?