If Truecaller detects your forward is still active but you are not Premium anymore, it will prevent the call to be forwarded back to your device after first decline.
Depending on the Advanced Caller ID option you have set, we really invite you to fully deactivate the feature at your carrier level.
Contact your carrier and ask to provide Conditional Call Forwarding code for Busy call
Contact your carrier and ask to provide Unconditional Call Forwarding code
Call these 2 number to ensure all configuration is reset
Please find deactivation country specific Carrier codes bellow: