I'm not entirely sure I understand the salary link to service base price? Is it essentially a [small] revenue share on top of a fixed salary? Or more like your salary gets a 5% increase when the service price gets a 5% increase, which is probably only a little bit above inflation. The second option sounds very unusual in a company with lots of customers and employees (and likely to significantly undervalue you if your skillset and responsibilities and the customer base have all grown).

Either way, it sounds like you should be considering your likely earning power in other roles with an equivalent level of seniority (even if it's just looking at this stage) as your skillset sounds likely to be considerably more advanced than the median IT/Telco employee in your city. That should be your fallback plan if you're not able to secure more than a token raise, not cutting your cost of living. This will of course also give you some basis for figuring out the bare minimum you can accept, so that you can pitch a counter offer (no point in flatly refusing) some way above that. If you expect promises tied to subjective metrics, tie them to objective metrics you know and they care about, or ask why not now?. It sounds like you've already figured the ways in which it's really in their interests to put some effort into satisfying you even if their natural instinct is to make a low first offer.