Product: Debt collection

Synter ( collection company ) sent us a demand for payment for XXXX XXXX. We paid the funds to XXXX XXXX. Then Synter started to send us other invoices from XXXX XXXX. I thought it odd because we didn't have any more and why weren't they included in the initial collection process. Through SEVERAL written notices of me demanding invoices ( after each collection email ) and them not sending them they finally sent the collection email to the correct company, which was a brewing company. I asked them several times to remove XXXX XXXX from these emails. Didn't happen. They still send us emails on a regular basis for the payment of the invoices that the brewing company owes. 
Email XX/XX/year> wrote to them to take XXXX XXXX off email as she doesn't work for XXXX XXXX any more - never corrected. 
Email XX/XX/year> - First email that included the XXXXXXXX XXXX, their invoices and employees included in the sent to and Cc. I asked for the invoices, just in case the invoices were ours, but they were never sent. 
XX/XX/year> - Another email from them still written out to both company 's empolyees, with the brewing company 's invoices - I replied with an email to request the invoices again so I could research. Never sent. I also again requested that XXXX XXXX be taken off the emails. 
XX/XX/year> - Another email from Synter requesting we pay the XXXX invoices. XX/XX/year> I replied to above and voicemail that we do not have the 3 invoices ( which belong to another company ). I told them to send the invoices and that they were not to contact me again ( both with emails and phone calls- they had been doing both for a long time ). I let them know I would report them. At this email, they took the brewing company 's employees off the email and were now sending directly to me and XXXX. 
XX/XX/year> - I had blocked Synter 's phone number and set up a rule to send them directly to deleted items. I also informed my superiors of what was going on. 
XX/XX/year> - Synter called again, I emailed them back stating that the invoice we owed for was paid. I asked them to stop harassing us. 
XX/XX/year> - They requested proof of payment for the one invoice that was ours and I sent it to them. 
XX/XX/year> - Synter again emailed and included me and XXXX, along with the XXXX XXXX 's employees. They were threatening legal action. I did not reply because it does no good. 
XX/XX/year> - Synter again emailed us, along with the brewing company 's employees, again requesting payment. 
XX/XX/year> - I replied that we have no record of the invoices. I again stated that if they couldn't send the invoices to stop contacting us. 
XX/XX/year> - They sent another email showing the debt is for XXXX XXXX XXXXXXXX XXXX The file number is XXXX. Our business is XXXX XXXX, they have no business sending us the email for someone else 's debt. In my reply, I asked them why they were sending XXXX XXXXXXXX invoice numbers and payment demands to XXXX XXXXXXXX XXXX XXXX I asked them wasn't it unethical. Turns out it is illegal. 
XX/XX/year> - Another email from Synter requesting that me and XXXX pay the bill for the brewing company. They did not include the brewing company employees. I replied that we did not have any dealings with the brewing company. I told them they were sending us demands that are none of our business. I asked them again to stop contacting us. I told them to email the brewing company and let them know I was reporting them to you.