Hi Beserithan,
Firstly, can you tell the TM version you are using? Also can you tell how many entries are you getting in it_res_calc_sheet paremeter when BADI is triggered?
Your approach of reading with "INDEX" may be a possible problem because system can have multiple responses coming back and you should make sure to add it in the right one.
You also have to be very sure about the MY_TCE_LINENR, system can't accept duplicates for this.
Thanks & Regards,
Tarun Kumar