R145 000 bill after underground water leak

We received an enormous water bill and immediately started to investigate, Joburg Water came out to test the meter in October 2014, said it was faulty and new meter was installed, at my cost. High water bill continued. Got leak detectors out and they found a massive leak under my house. This was fixed immediately. Have letters from leak detectors explaining why this happened and that they cannot keep the property owner liable for this. Joburg water has billed us R144 000-00 for the water leak. We have mailed them probably 30 mails regarding this since October 2014 until now, with absolutely NO reply from them. We are renting out the house and we do not live in SA, so we cannot go to Joburg Water's offices to sort this out. Tried a few times to phone them from overseas, but you just hold on forever. The water bill is just escalating every month because over the interest they are charging. But still absolutely no reply whatsoever from them!!!! I have absolutely no idea where to go from here, they cannot expect anybody to pay this amount for water due to an underground water leak!!!