You get a limited amount of time in which to achieve the same level of trade pay you held in your original trade; during this time your wages do not change. Once this period has elapsed, unless you have gained the necessary trade qualifications and pay parity...
You are too vague about all this for me to provide decent advice but:
If you have been paid at the wrong rate, and the settlement they have paid you does not cover the amount you are owed; they clearly need to pay you more... Who is fobbing you off? Ask for copies of your pay statements and point out the errors.
By retrading, this does not affect any pay that you have already earned but that they have not paid you correctly. As I said previously, when you retrade, you get a limited amount of time to achieve the equivelant trade quals; once that has elapsed your wages can be dropped.
You need to start sorting this out with your pay staff; if they do not sort this out; you should approach your chain of comand for their help (Section Comd/Tp Sgt/SSM/OC etc...)
I retraded from the Sigs to the QARANC to do nurse training which is three years. I was a L/cpl band 3 cl 2 and was told initially that I would keep my trade pay for six months. This they extended for 2 years. Before this period ended pay(cut) 2000 kicked in so I managed to see my training out on a decent wage.
I hope, for your sake, this 2 year rule still applies and that you get as much money from the b@stards as you can.