Actually you will (if I remember correctly) also have to have the iMageMagick PECL enabled in PHP. as I said in an earlier post.
If you have access to the command line of the server by SSH then you can see what is loaded with the command php -m
command.
View attachment 266093
If you are using a shared hosting or a control panel it should also be able to show you what modules/PECL's are loaded there.