Indexed, though blocked by robots.txt

I am working on an e-commerce website (similar to e-bay) where users can buy or sell products.

The urls for buying a product are like:

my-site/browse/cars my-site/browse/toys etc 

And the urls for selling products are like:

my-site/post-ad/cars my-site/post-ad/toys etc 

When selling a product, user just need to fill a form and click on Save. Also user needs to be logged-in, in order to sell a product, therefore I have decided to prevent this page from being crawled and added the following to my robots.txt

Allow: /  Disallow: /*/post-ad Disallow: /account/login?ReturnUrl=* 

Now I am getting the following warning in Google Search Console, for of of the post-ad pages:

Indexed, though blocked by robots.txt

How can I resolve this issue?