You can quit however you'd if you aren't planning to go back there. Say it doesn't seem like a good fit, can mention all the messed up scheduling (but they could try to tell you it's a one time thing and convince you to stay), make an excuse saying it has been so long you found something else, could just cut contact with them (but might make training pay difficult).

Could do it all in one message, "Sorry xx, but I have to pass on the position. Due to the delays I've been offered another job that's closer to home, and the training schedule change makes me unavailable for an appointment I already had. Here is my information for x hours of training videos (SIN, void cheque). Sorry it didn't work out."