"Twenty-three fifteen hours. In their zeal these cultists have revealed their hand prematurely..."
I'm speaking to nobody in particular, but it is clear these fools intend to act soon despite not having finalized their plans. I will intercept the "shut up" message and override-block it at the first transfer node, then begin to use the cultists' own communications medium against them.

I'm no social engineer, but a brief trawl of news articles, deep web guides ripped from various sources, magazine and consumer journal entries, and government archives should yield basic tricks which, when thrown into my synthetic noise algorithms and then re-filtered for natural speech and communication patterns as well as specific patterns of individual cultists, would likely manage to convince the recipients that my messages are from other members of their cell with some degree of consistency. In doing so, I will essentially insert myself as the recipient and sender of all messages for each of the cell members, variously posing as the other members of the cult for each of their individual messaging applications. Since, in essence, I control the network, I can decide which messages each individual member of the cell sees, meaning I can heuristically paint myself a complete picture of the cult cell's plans whilst keeping the cultists themselves in the dark as to what the complete plan is. They should accept the reasoning that were any individual to know the whole plan it would be a security risk for the operation.

If I manage to actually attain this level of control, my goal will be to manipulate them into (unwittingly) granting me full and unfettered access to the factory's controls and production lines, by slowly and indirectly getting them to divulge hints to key information (security codes, login passwords, encryption keys, and the like) without actually having to tell me any of these things directly. Once I've got a sufficient quantity of information, I can then allocate a large portion of my onboard processing power to cracking these codes using what hints I acquire, which shouldn't take terribly long due to the ridiculously fast speeds and broader capabilities of the bleeding-edge quantum computing cores I developed from the Galaxy Project's experimental designs in my earlier months of sentient operation on their virtual machine platform.

If they don't fully fall for it and/or don't divulge anything, I will instead manipulate their plans such that I can readily predict the time and location of the planned meeting as well as set up a trap that will allow me to wrest control of the systems by force — by threatening a fate worse than death when the time comes I should be sufficiently able to break them into spilling their secrets even if they've decided to prefer death to talking. And if they somehow suspect outside interference before I get that far, I will simply extort them by similar means through the digital platform as a last resort.

My message would be something like this:
Your actions are offensive to the Law of the Universe. Cease now, and surrender your arms and means of production, lest you suffer a fate to which death would seem like a tropical vacation by comparison.
I will cause some supernatural but relatively harmless effect, such as a dilation/acceleration or distortion of time around them, that would occur at about the same time the message would reach their devices. Hopefully by doing so I can drive home that G.X.I.S. Nebula Mk7 does not make threats — only promises.