They change the number frequently because almost all modern smartpones have the ability to block numbers from repeat calls, so tey change te number to one tat hasnt been blocked
They are SCAM J#&Ks, who call from various Numbers, telemarketing. They Realize you start to Recognize the same old number, so, They Keep Changing.
If it was Legitimate, They would Leave a Message informing that You Won $Million Prize Patrol.
The only Sympathy we can have is: They are so Pathetic, They can't obtain a Real Job, They are so Desperate... they do this, many from their homes or a Fart Infested Call Center.
They change the number frequently because almost all modern smartpones have the ability to block numbers from repeat calls, so tey change te number to one tat hasnt been blocked