GDPR has lots of issues and this is one of the major ones.
It can be easily argued that companies cannot be forced to service users and there has been no real precedent or enforcement around this.
Consent is a voluntary action. Usage itself is a form of consent. However a user disagreeing with what the company requires to provide that service but still being entitled to and actively using that service is not workable. User can decide to stop using a service entirely though, if they don't agree with the requirements.
That's meaningless. Usage is already a form of consent. The discrepancy is between the user and the company in what is consented. Forcing the company to provide service to the user even if the user disagrees with an upfront description of what the company requires to provide that service is a completely valid objection.
Also GDPR applies to any organization providing to citizens of the EU, not companies operating there, but that's yet another example of poor design which results in GDPR having little enforcement.