It would be helpful if you could answer the questions we've already asked you, please. You have only hinted that the jurisdiction is England & Wales. We also need to know if you have any previous convictions.
As you have given a guilty plea already, then much of the room for negotiation has been given up, so I see little opportunity for an agreement which avoids prosecution. It's possible that a lawyer representing you will be able to agree a settlement, perhaps at the last minute, but more likely they will not, and can only give the mitigating grounds about lack of money to try to minimise the sentence; however I have to say that I don't expect that will be very helpful either, as it will be clear to the Court that someone without money shouldn't use services that cost money. Attempting to defraud a Company is a serious offence - if it is an Offence under the Fraud Act that you have admited - carrying the potential for 6months imprisonment. In mitigation this can be averted and a fine or community order imposed.
I assume that you have made no 'restitution' (i.e. repayment of the monies you have deprived Northern Rail). If you had, this can reduce a sentence under the Fraud Act.
An Offence under the Railways legislation will probably carry only a fine in your case, though you will still be expected to compensate the Company for the loss of revenue.
Now, please give us the details.