Welcome to the community!
I think everyone is rather fed up about getting SPAM and SCAM calls. You should note that blocking the calls on your phone only rejects the calls so they go unanswered. As you are aware, it does not prevent the callers from leaving voicemail. That's because unanswered calls get sent to voicemail . The only way to prevent callers from leaving voicemail would be to block the phone numbers at the network level. However, as you may be aware, the calls are being made using spoofed numbers.
Unfortunately, there currently isn't much that any of the mobile providers can do to prevent them. Since the spammers/scammers use spoofed numbers, it is not possible to identify the true spammers' number. The numbers shown on caller ID do not belong to the spammers. They often belong to innocent, unsuspecting people. There isn't much that can be done to prevent numbers from being spoofed. In some instances, the spammers/scammers will use the recipients' own phone numbers to make the calls. Even the RCMP are not immune to being spoofed (see here).
Blocking the spoofed numbers at the network level is not feasible. Blocking innocent customers for no reason is not acceptable. That's why the mobile providers and landline providers simply cannot block a number without absolute proof that the owner of the number is engaged in nefarious activities. Blocking numbers simply based on their apparent use to make SPAM calls or send SPAM SMS would result in honest customers having difficulties using their services.
I understand some apps might offer that service. However, those blocking lists only affect people who opt to use those apps. Honest customers who might actually own those numbers can still use their services, just not to call people using those apps. If a mobile provider were to do the same, honest customers would have difficulties using their services.
The mobile providers have implemented Universal Call Blocking which is meant to block calls from malformed phone numbers. That said, I'm doubtful whether it will have much of an effect on the amount of SPAM or SCAM calls since many of them appear to have properly formed phone numbers. In addition, a new technology, STIR/SHAKEN (Secure Telephone Identity Revisited/Signature-based Handling of Asserted Information Using Tokens) is being adopted to further reduce the amount of nuisance calls (see here). However, I have my doubts as to whether those measures will reduce the amount of SPAM calls. My understanding is the STIR/SHAKEN will only identify possible SPAM calls and mark the calls as suspected SPAM.
Unfortunately, until the technology to unmask the true number of spammers/scammers is readily available (not simply the number shown on the caller ID), the only solution currently is to block the numbers on your phone. There are (at least were) some apps which claimed to also prevent callers from leaving voicemail. They worked by answering and almost simultaneously ending the calls. While those apps do prevent calls from going to voicemail, the calls are also considered 'answered' and therefore count as airtime.
Hope this helps 😀