Received XXXX services from XX/XX/XXXX-XX/XX/XXXX. XXXX received in XX/XX/XXXX did not appear to have proper insurance reimbursement and network adjustment through XXXX. Contacted XXXX and provider. XXXX response was unclear but blocked further inquiry. Began monthly letters to provider ( XXXX XXXX ) asking for clarification of charges. Provider only responded with additional invoices which had different amounts almost monthly. Received occasional phone calls from provider rep who agreed to look into the account but never submitted requested information. Engaged a medical billing dispute firm in XX/XX/XXXX. They also did not get the requested information. 
Today we received a notice from a collection agency in Wisconsin who asserted that they had been retained to collect the amount due, now shown as {$2100.00}. We had not been advised that this action was pending. Sent certified letter to that collection agency stating that the account is and has been in dispute since XX/XX/XXXX. We are basically being asked to pay an amount that they say is due without providing any substantiation. We are able to pay and have offered to do so with validation of the amount due. Total lack of response and responsibility by provider. May simply be a matter of how the charges were coded for insurance reimbursement ; but they have been unwilling to take necessary steps or provide the information that we requested.