Visual editor keeps stripping my <a> tags

My first post, please forgive me if I'm doing it wrong.

For some reason when switching to the visual editor WordPress will strip out my a tags. "Don't use the visual editor" isn't an option, I'm making a website for clients and I'm trying to make it foolproof. I don't want them to be able to go to the visual editor and accidentally have all the links stripped out.

This is a sample of the code. When switching to visual and back to text, everything is there but the a tags.

a href="https://www.url.ca" target="_blank" title="Donate Now"
div class="donate-now"
div class="wred"
h1Click here to Donate Now/h1
div class="wbumpred" /div
/div
/div
/a

class="wred" styles a background colour and shape.
class="wbumpred" adds a small graphic element to the bottom of the "wred" element.

Please help!

Thanks,
Sarah