For what I understand, without looking at your logs, it could be like this:
Code:
_xxxxxxxx 0047${EXTEN} voipbuster.com
_001X. ${EXTEN:2} voipbuster.com
_00X. ${EXTEN} voipbuster.com
This way, in rule 2 the leading 00 is stripped, I assume your provider expects a leading 1 because otherwise rule 3 would cover this cae.
Without the X, maybe your rules expect more ones or zeros!