I'm sure that most reasons as to why you have not yet been signed on have been explored here; I just thought my experience may be of some interest.
When I was promoted last it took me a while to convince the powers that be to make me substantive, I believed that promotion from Sgt to CT had no "Acting" rank in the process, however after not receiving my increase in pay for about four months I started banging on the JPA door, after many a frustrating attempt to speak to someone from the mythical "back office" I finally was told that I was only acting CT pending system update by the Promotions Cell at PMA. I then set about finding someone at PMA/ACOS Manning who may be of some help or at least interested. After further two months of pestering I eventually found out that because I hadn't completed the multiskilling package I could not advance in rank as that was a condition of promotion! Fortunately I had retained the copy of the X annotation form that I had received after taking some poxy leckie exam that now qualifies me less than I was as a proper splitter, and faxed it off to them. Pretty quickly JPA was amended correctly and my back pay arrived in the following pay chit.
The lesson being is that I suggest that you and all your fellow Acting Cpls check that you have actually completed all of the prerequisite quals that are associated with substantive promotion within your trade. I would suggest that you raise a JPA query on line, as once you right to them officially they tend to reply giving you quite succinct answers; just make your questions to them as plain as possible.
Good luck!