I get the sense that this reporting is trying to lean heavily on the usual implications of “refusing to pay the bill”, which is that one can’t pay the bill. But that implication obviously isn’t at play here; Google Cloud isn’t worried that Twitter is broke.
In all likelihood what’s actually happening is that Google Cloud strongly expects the new contract to be less profitable for them, and thus they wish to delay and drag out re-negotiations so they can have the more profitable contract for longer. Refusal to pay invites a lawsuit; if the cost of the lawsuit exceeds the profit that would be gained by holding onto the old contract for longer, it makes more sense to re-negotiate now. I predict Google Cloud will launch a token lawsuit for non-payment and come to the negotiation table at the same time, and when new terms are agreed on Twitter will settle the lawsuit by paying the old contract rates up to the date of the new contract.