This letter complains to an online service that you can't dial onto their service because of busy signals.
1234, Main Street
Boston, MA 02123
01 April, 2005
<Recipient Address Goes Here>
I became a customer of <company name> <time you became a customer>, and have had no problems with your <Internet/online> service. However, I have recently experienced constant problems dialing into your system, problems which keep me from getting online most of the time.
<your need for using the Internet>. Not being able to access your service is real hardship. Please contact me with any suggestions you may have about getting online more easily.
I look forward to hearing from you. Thank you for your time.
encl: <List of enclosed items goes here>