When this happened to me, I used a piece of wood against the bolt handle where it attaches to the bolt (strongest point). Tapping gently and repeatedly the bolt slowly worked its way back. Once there, I used a razor blade knife across the face of the magazine to cut the lead pellet. Once the magazine was free I used a wooden dowel (not a metal cleaning rod) to slowly tap back what was left of the pellets.
Go slow and you might be able to save the magazine.
~ Mondo

Remove the barrel first and see if that helps

A word of warning to anyone getting into this situation again, especially thoses who may be using the Huma V2 dual port, transfer port.
You can manage to snap the brass bridge in the transfer port from forcing the bolt to shut.
the best way to clear a blockage would be to loosen and pull forward the the barrel by a few mm first, then to remove the magazine. this prevents the chances of a pellet falling into the TP hole within the rifle's action. then pull the barrel out and carefully remove the pellets with a rod. this may save the transfer port.