After looking at two other posts, I modified your writing like this:
Hi Mark,
I am still doing my old job. What troubles me is the fact that when I try to keep the accounts updated, sometimes I am putting the same CIS invoices into the system.
I just have noticed that two invoices with the numbers X2006015 and X2006025 were recorded paid but are shown to be missing in the system, so please send me the copies of those invoices.
If there is anything urgent, please contact me other ways. I will let you know when I start to work full time in my new job/employment.
Kind Regards,
I think putting the word "job" under two different contexts makes the writing ambiguous.