Not sure of the type of plastic,shape ect. but you can use a wire to cut through plastic by simply heating it with an electric current.
A couple of alligator clips,some heavy "lead wire" and a thinner cutting wire and a power source are all you need. However the "hacksaw" will work and a Sawzall with a metal blade will make short work of it. Another method would involve a trim router, but, as you said, you don't have the tools.
I worked with acrylics for awhile, and we cut it with various things depending on the thickness and what needed to be done, cutting with a heated wire let you make bandsaw-type cuts that were as smooth as the product.
The above is an excellent posting of yours from 2012 on cutting through hard plastic with a hot wire.
I just need clarification on two points --
(1) what type of power supply?
-- Obviously, 120VAC wall current is not only dangerous, but would probably be too hot and would likely trip a circuit breaker immediately unless the cutting wire was so thin as to also be easily breakable.
-- Would a doorbell transformer (16 VAC) be a way to go?
-- How about low AC or DC voltage from a "wall wart" transformer? -- I have lots of them, from 3V to 20V.
-- I'm an electrician who needs to trim both sides of a plastic switchplate to fit into a narrow space with straight sides, so I would have no trouble creating or adapting whatever is needed.
(2) How do I keep the heated wire straight while cutting?
-- Holding it stiffly in gloved hands somehow is an invitation for disaster with my inherent "gracefulness", so what kind of wire holder should I try to fabricate?
