pptp server over ddns address

I have a mikrotik routerboard with enabled pptp server running succesfully on it.

The mikrotik is connected through wan from a dsl modem before it.

The dsl has a ddns service running on it.

Trying to connect to vpn pptp server from my mobile phone “android” using the ddns address on my dsl modem and port forwarded tcp 1723 on the dsl modem to the mikrotik’s ip assigned by dsl modem.

Not working. Any ideas ?

Note: firwall rules are created for gre 47 protocol and port 1723 on the mikrotik router successfully.

Do you forward also gre on the modem to the router? Anyway you should use transparent bridge mode on the modem and let router to connect directly thru the modem.