I am glad you have reached out to the community, I can understand how frustrating that would be.
If the co-owner is your spouse, I would recommend to check both of your returns, to ensure that it has not been double reported, which would make it appear that you are claiming 100%.
An easy way to check for this, is to review your forms. If in Easystep mode, Click on Forms, and then click on forms at the bottom of the screen to see all of your forms for your returns. You will want to look for T776 and verify that there is only one form.
On the form, you should see your portion, of the total income, reported on line 9946.