DTMF issue while dial in/out pin code and some time extensions, this is very common issue and you can solve it easly.

It's not asterisk problem. It's your provider....
And the dtmf mode as if you are using dtfmmode=inband and the provider did something with their system and now all of a sudden it doesn't work.
try to use rfc2833 it is common mostly used by VoIP providers.

dtmfmode=rfc2833
canreinvite=yes

And if that doesn't work-

one more thing you can:

dtmfmode=auto (it works)

if still you are not able to go throught then who is your provider? check their portal or create trouble ticket there.