Shady business practices

I ordered Teamviewer online on Nov 2015. They sent me an invoice and I tried to get it paid by my company. But they could not do so in time so I went online and ordered using my credit card. After a while I started receiving emails that I did not make payment on the invoice they sent me. As I had already purchased it by another means I ignored it and assumed as per their terms in their invoice they would cancel the invoice (payable until 14-Dec-2015). After a while they were still sending me requests for payment and I let them know that I have bought it already and they must please stop sending me reminders to pay this invoice. <br> To my great shock I got this back:<br> <br> It is a fact that you've entered into a purchase agreement and it does not matter if the license has been used or not.<br> <br> You had ample time within the 7 days money back guarantee period to inform us about this.<br> <br> Please communicate further payment issues with the debt collection agency in SA when they will contact you in the future. <br> <br> They actually want me to buy it twice and are threatening me to pay up even though I have bought it already. This is seriously shoddy business practices and I will never use them again.