Unacceptable service

Well were do I as a supplier begin... I placed an order and paid in full on the 5th of December 2018, we are on 25th of Jan 2019 and still no delivery. It takes them 7 days to co,e back with artwork issues. I have on a 100 or more accusations requested that someone assist me with the artwork they have a problem with. Last Friday the 18th Jan 2018 a lady phoned me and we changed the artwork according to the specs. 7 days later I get a mail to inform me that the artwork is still not correct. After they had my file with the "manager" whom confirmed that the artwork was fine. Now I gave them till close of business today to get back to me with no avail. I would like to know how can they have my money in their back account pulling interest on it and I have no product to deliver to my client. I work with big suppliers and never before did I need to wait 7 days for an e mail on artwork changes. I have other suppliers that from order placed to delivery 2 days. I need to get an answer regarding the above, for I have a client I have to supply.