Dear Chap,
It just so happens I had exactly this problem about 2yrs ago with an old employer of mine.
They insisted I pay back all the outstanding bond in one lump sum. After I sought council on this matter it appears that if you don't have all money, and you agree on the amount owed AND you have offered a monthly payment, there is no case to answer to.
Just so you're sure, this is exactly what I went through. If you need legal advice I can point you in the right direction to a chap recommended by the IPA. Just let me know here.
Above all, remember, if you agree on the amount owed, there is no case.
Good luck old chap............