Google Calender for wordpress.com blog

I keep going round in circles with this one.

I want to embed a google calender into my blog. I understand that the way to do it is via the method shown in

https://en.support.wordpress.com/google-calendar/

but when I do it, the embed code doesn’t appear, it just strips out the iframe tags and leaves a link.

Can someone tell me the right way to go about this? Having a wordpress.com blog means I can’t use a plugin.