Whistlephone SIP

Hi,
I’m trying to configure a whistlephone trunk for a week now whithout success. The particularity f fthis provider is that all 4 proxys need to be registered for this to work correctly. If not, we have the infamous “sorry but we cannot connect your call”.
Now, in in PiAF (FreePBX 2.8.1.3), I created 4 separate trunks WP_1 to WP_4 as follows:

context=whistlephone-incoming
type=peer
disallow=all
allow=ulaw
dtmfmode=rfc2833
host=proxy1.whistlephone.com
insecure=port,invite
fromuser=myDID
authuser=myDID
username=myDID
secret=mysecret
canreinvite=no
callerid=myDID

Same for proxy2 to proxy4.

Under Register string I have this:
myDID:[email protected]/myDID
I also created an extension that points to my ATA. The whole setup doesnt work, still getting “I’m sorry but I cannot complete your call”. I’m kind of lost here. Any help welcome.
Thanks