Herceptin

After having my operation to remove lump from my breast, I received chemotherapy then radiotherapy and now on my 7th doze of herceptin. I was told I would need 18 in total, 1 every 3 weeks for a year, but now they are saying we only need 9 and will stop in 6 months. 

I'm worried this is due to coronavirus and funding and dropping my treatment by half is a risk to my health.

Can I demand I still get 18 as this is what I was told after my diagnosis in july 2019?

Many thanks.

Kaz.