I'd make the following recommendations:
- go to the meeting: if you don't, you break your record of full co-operation, which can only be bad for you
- if you're really uncomfortable at the prospect, bring someone along with you: they don't have to say anything (and really shouldn't), but their physical presence can be a help
- go with the objective of listening to what they have to say, not to reach agreement
- listen to what they have to say: they asked for the meeting
- take plenty of notes, and do so openly. If you have brought someone along, they can help with this.
- outline your own position, as in your original post here: don't forget you're in a much better position that most of the people in arrears. If 50 a month on top of the full repayment amount is all you can afford, then state it
- do not negotiate! if they make a proposal, take a note of it and say you'll get back to them after you've had time to consider
- after the meeting, write up your notes, and send them a copy as a record of the meeting. Put in a statement that unless you hear anything in relation to the notes within 5 days, you will take it that they are agreeing it is an accurate record of the meeting
Good luck!