Free services have no reason to exist without advertising.

This is at the very least not obvious. Advertising does, again at least not obviously, increase the amount of money consumers [can] spend. If they shift money to one product, another one will see reduced consumption and get more expensive to manufacture.

Also what prevents one or a few companies from being very successful with their advertisement, becoming a oligopoly or even a monopoly and then inflating the price for more profit and to the disadvantage of the consumers?

I think this is just as muddy as the bits you pointed out. Incumbents don't need to advertise but new players do and they have a better chance to gain market share with targeted advertising due to more effective use of their often limited budgets.

You are of course right, I only wanted to given some scenario with opposite outcome for customers. My point was more that one will have to provide much better arguments or evidence than some random macroeconomic interaction to convince me that advertising has any net positive effect.