Adam, you're doing the right thing by inquiring about your wages. Don't listen to these guys, they'd have you working for nothing like an intern for a politician if they had their way!!!
You are doing nothing wrong and BTW, you cannot be sacked for asking genuine questions about your apprenticeship as they have signed an agreement to train you and have a duty to fulfill this in it's entirety!
So well done to you, for NOT listening to the nay sayers that predict doom and gloom if you ask a reasonable question.
Lastly, join the union and become a member alongside all your other electrical brothers, stay in it no matter what you hear about them (and you'll hear a lot of mis-information over the coming years!), and even though you will jump between multiple companies you will always have that bond with the rest of us that you are a member of the electricians union and no company can stop you!!!
N.B. just an observation, but it's good to read a thread relating to a real JIB apprentice for once and just shows that there is apprenticeships on offer and not just fast track courses!