Will / will not + infinitive is used when we talk about spontaneous decisions
We can express determinations or strengthen the decision be using will/will not.
It is possible to use will for very formal arrangements.
Shall + I/we in contemporary English is used when we ask about decisions.
I/we + shall/shall not express determination in a formal context. There has been a significant change in the contract.
be going to + infinitive to talk about intentions or things that we have already decided to do.
We avoid using go and come with be going to.