Nothing you did to the engine should cause that much blowby and that low of compression.. That is completely thier fault!
^ based off of what i already know
I would bitch and moan in thier managers face until you get a COMPLETE rebuild for no charge! that is absolutely rediculous! What kind of place are they running if the engine breaks down after 20k! What is the coverage on the engine? What are the terms/conditions? you might be screwed if it says anything about engine modification, cause that may void the warranty.