How can I get my DS to poop in the toilet?

[Jad]

I know this is probably an issue many mums face, but I feel that after a year, I'm finally reaching the end of my teether!
I potty trained my DS a year ago, but he point blank refuses to poop in the toilet. For most of the last year he has held his number 2s for a week at at time. It is only when he can't hold it any longer that he finally goes - but always in his pants.
I have tried the star chart, and being cross, but neither have worked.
I thought I was getting somewhere last week, when I resorted to blackmail, (small gifts wrapped up, in view, for good boys who use the toilet).This has worked well since last week. He has since gone every day, and mostly in the toliet, but today he resorted back to the old norm of using his pants.

What can I do? Can anyone please give me some advice?

how old is he Jad

He's 3.5yrs

I had to use mini choc bars as a bribe to get ds to do it in the toilet at age 3.He still won't sit on the big seat without the padded child's seat,so can't do a poo outside the home....sigh .

I'm relieved to know that someone else used bribes.