Show up to court...along with all of your receipts.
The only way that they can get a judgement against you, is if they worked out a payment plan with you and you have defaulted on the payment plan.
However, if you are paying as agreed, and can prove that, a judge will dismiss their case. They would actually have to lie to the court in order to even file it, b/c they would have to say that they are not receiving anything from you to even get a judgement.
Call them back, and be very clear that if they sue you, what your address is, because you fully intend to show up...receipts in hand.