*********** Impact Meter Services accuses wrongfully of non-payment!

I have always paid my water bill timeously. As soon as I receive it, I pay it. I have paid my February account, but am being accused of not having paid it. After several calls to Impact Meter Services, I am unable to speak to their accounts department. I have emailed them more than 5 times, attaching proof of payment, yet they keep asking me for it, keep sending emails and SMSs accusing me of non-payment even after they HAVE THE PROOF WHICH I HAVE MAILED TO THEM FROM 2 SEPARATE EMAILS!