Harassing for null and void collection

Being harassed for an invoice that was issued to me before I gave the go ahead on licence renewal and even after requesting several times that the invoice should be credited and that I was no longer making use of their accounting software it is still being requested for settlement a YEAR LATER! I haven't received a new licence code so no services were rendered.....

When replying to the debt follow up I am met with this message: "Your message wasn't delivered to ********** because the address couldn't be found, or is unable to receive mail."

Very Frustrated and solidifies my resolve to not support the company again and not to recommend their products.