Invoice problem

Hi 

I keep getting emails stating I have not paid an invoice this has gone on for months. However, I paid the invoice soon after receiving it and have proof of this. I keep communicating eiother by phone or email and providing evidence but still get the emails. 

Is there a number I can contact who could help me I have been given +90 02123776056 but this is a restricted number on my network.

Not impressed with the service from booking.com 

Anyone else had this problem and if so how did you resolve?

Thanks in advance

Michael