Not allowed to make a payment arrangement

I received an email from Landau Attorneys last year, for my outstanding Wonga loan of R3913 that needed to be settled on Monday 10 November 2014. I advised that I would not be able to make the payment and asked to make 4 payments from the 28th of November 2014, my final payment being the 28th of February 2015. I was told that the only terms of payments are to settlement amount or half as that's the only options they have. I advised that my hands were tied and there was nothing else I could do, until my financial state changes.<br> <br> I have not heard from Landau Attorneys, and my worry is the interest on this debt. I did not refuse to pay the account and still have the emails. What must I do now if I'm not even allowed to make small payments towards my debt? Is this how clients are treated?