plz help me !

hallo , i had maked so many Accounts with BetaMax Prgramms like webcalldirect,Internetcalls,Voipcheap.....ect and all of them have worked for some time and then stop !!! im really disapointed , i have always trusted this Service and always bought credits !! i receive alaways this Error Message :call ended (the other party ended the call due to unknown error) plz find a solution for me ! Thank u very much Kind regards Manar Osman