There is several ways of doing this,

1. use FILTHS code post
that is awesome at making prestiges stick,

2. use a infectable menu off some

3. Trying to derank can be tricky so, if u are using motion flex, the code post is what counts, if u can get the code pot that got released with PHOENIX menu then that one is also pretty good at making it stick, try it a few times and one of them times it should stick, to do it several times, do a lobby, do ur prestige, RESTART, then do that about 4 times then go to multiplayer too see if that worked,

hope this helps pm me if u want me to help u more

ill inv you tonight, PM me so we know when to get on.

i heard if u delete the gamerpic that u get in a lobby it helps the process