Changing landline number may be useful if you wish to break contact with a person/people who are known to you.
When you change numbers though, you simply receive a 'new' number from a general pool of numbers which belongs to VM.
We have seen past topics on here where a customer has changed number to try to eliminate receiving general spam/scam calls only to find that they restarted shortly after the 'new' number was put into use. Scam calls are regularly generated in bulk using automated diallers which dial all number in a range in turn so even a 'new' VM number is likely to receive scam calls eventually.
