If the train has arrived at the destination then u cannot cancel the tkt, u need to file TDR
Also personal experience, u need to cancel from the prs of ur boarding station after chart prepration
I had 2 tkts from PNME to NDLS
One in 12301 with waiting which got confirmed
Seconed...
more... in 12801 which remained in wl so when i went ot GRD prs he said PNME prs se hi cancel hoga yahan pe chart prepration ke baad nahi hota hai
One more instance was in 12303 , tkt from MDP to NDLS
Tkt didnt confirmed so i went to GRD prs he said MDP prs se cancel hoga wo bhi train ke delhi pahunchne se pehle pehle tak after that TDR