How to Unblock UDP Ports which has been blocked by ISP for VOIP

[threeplanet]

Hello,
I have been using this(VOIP) net to phone device PAP2 and suddenly my ISP has blocked the ports and I m not able to call anywhere. Is there any soultion regarding that. Please tell me what changes I can make from My side and also I can ask the company to make changes on there server which provides us VOIP service.
Thank you