Unless you had a written agreement which can be produced as evidence I suspect your chances of getting any money back are sadly minimal. If you did have a written agreement, I suggest you write to him first giving him a deadling for reinstating the standing order, saying that you will take him to court. (I'm unsure what the upper limit for sueing is in the small claims court but Googling this information will probably provide an answer). If you have no written agreement, I fear you might as well write the balance off.