Why is my mandarin tree not flowering?

[elsie2023]

 

I have a grafted mandarin tree which has been in the ground for almost 3 years. It has never had any flowers. I feed it with blood and bone and citrus fertiliser however it didn’t make any difference. 

Could it be the rootstock overtaking the grated mandarin tree? I do see a graft line at the bottom but there are 2 identical trunks.

[elsie2023]

Thank you so much for the valuable advice! I guess I will replace it with a real mandarin tree.