My electricians messed up and installed some sort of camera (or very old cat3?) cables, instead of the requested ethernet cables (see picture). Now I have two of those, running for about 15 meters behind walls and recessed ceilings, making it replacing them very costly.
Is there a way to still use them - grabbing 8 of the cables for gigabit connection and the remaining 4 for a 100mbps connection or some sort of other arrangement?
That three-pair TP(?) cable doesn't look like any cable category, more like a basic signalling cable - a giveaway is an unmarked cable. It might not even have properly twisted pairs.
That's not very likely to reliably run a network connection. A short run could perhaps transport 10BASE-T and possibly even 100BASE-TX. It requires proper pairing in any case, you can't just pair any two wires. But that's not anything a professional network could use. I'm afraid you'll need to replace.
While you're at it you should consider using empty ducting to enable easy cable replacement.
