If you or anyone else are doing on-call for no additional pay, precisely nobody is forcing you to do that. Renegotiate, or switch jobs. It was either disclosed up front or you missed your chance to say “sorry, no” when asked to do additional work without additional pay. This is not a problem with on call but a problem with spineless people-pleasers.
Every business will ask you for a better deal for them. If you say “sure” to everything you’re naturally going to lose out. It’s a mistake to do so, obviously.
An employee’s lack of boundaries is not an employer’s fault.