You could do what I do, ignore ThingsSpeak and similar services and simply run your own system on a webserver, you may already have your own domain name which also provides server space?. Then you write the control software on the server, using PHP and MySql, and call a PHP script with GET.
A big advantage is that the remote part can be kept simple, and the PHP scripts can do all the clever work - so you can easily upgrade the system by simply altering the PHP/MySql on your server.