If your company has a fixed format for R&R letter then you could write them a formal email inquiring about it. Print your email and there reply as a part of attachment.
Secondly, you could ask your senior colleague or your director under whom you were working with your first NOC to write your responsibilities for that particular job.
If your boss and colleagues are not changed then The same colleague could write a second letter stating your new job responsibilities and the date when your responsibilities were in effect !.
OR OR
The same colleague could write the same letter as HR wrote above, and make segregation between the responsibilities above, under 2 NOCs. You will take that letter, the letter from HR, the email saying they have fixed format and can not segregate.
Write an email wisely, stating CIC concerns and get their formal reply.
I have done that in past.. For example you could write "Dear Mr/Mrs. As per our last conversation you have clarified that you can not give me two letters for the two different titles I have held. As you know I was working under this title during this period, and later shifted to this title, I would appreciate If there could be a way or an exception for me to get a letter for both of the positions I have held. Stating my responsibilities for the two different responsibilities I have held is important for me, and I would appreciate if such letters could be issued. Moreover, within these letter could you please specify that the working hours are 40 hours/week as it will also help me with --- put something here, or wisely ask this."
There reply to this would help CIC understand that you have tried your best to get things, and that you were working under two NOCs and your employer has refused to write that etc..
I hope it would clarify many things for you.
Best Regards and Good luck!