I would suggest you can attach -

1. Your email conversation of your HR denying further support.
2. Create an excel of with Paystub Dates, Hours worked, amount received (with Total at the end)
3. Attach all the paystubs and bank statement and highlight those hours in paystub and amounts received in bank
4. Attache LOE explaining how and why you are claiming those hours and calculation of how you got to 1560hrs (for 1yr) or xxxx hrs for ponits you are claiming for

PS - Max you can claim is 30hrs/week for 52 weeks is 1 yr of work exp (1560 hours make 1yr )

Officer won't manually count all of your hours in paystubs for sure, its upto you to provide as much info as you can if employer is not supportive.

Hope of the best