after switching carriers all my calls go straight to voicemail

Two common causes after a switch. Old call forwarding left on the line. Dial ##002# and press call, that clears all forwarding on most networks. Then make a test call from another phone. Or a phone setting: on iPhone check Silence Unknown Callers and any Focus mode, on Android check Do Not Disturb and call barring. If none of that does it, the number transfer might not be fully finished, your new carrier can see that on their side.