Setup manually Ja Mobil APN Settings for your device. This is Ja Mobil 4G+ APN Settings which is updated.
Ja Mobil APN Settings
Ja Mobil APN Settings

How to setup Ja Mobil APN Settings for Android?
In your Android mobile/Tab Go to Settings > More >Cellular/MObile Network > Access point Names > + ( to add)

Ja Mobil APN Settings for Android

Name : Ja Mobil
APN : internet.t-mobile
Proxy : Not Set
Port : Not Set
Username : t-mobile
Password : tm
Server : Not Set
MMSC : Not Set
MMS Proxy : Not Set
MMS Port : Not Set
MCC : (Keep default)
MNC : (Keep default)
Authentication Type : Not Set
APN type : default
APN protocol: Ipv4
APN roaming protocol: Ipv4
Enable/disable APN: APN Enabled
Bearer: Unspecified
MVNO type : None
MVNO Value : Not set

Ja Mobil MMS Settings

Name : Ja Mobil MMS
APN : internet.t-mobile
Proxy : Not Set
Port : Not Set
Username : t-mobile
Password : tm
Server : Not Set
MMSC :  http://mms.t-online.de/servlets/mms
MMS Proxy : 172.028.023.131
MMS Port : 8080
MCC : (Keep default)
MNC : (Keep default)
Authentication Type : Not Set
APN type : mms
APN protocol: Ipv4
APN roaming protocol: Ipv4
Enable/disable APN: APN Enabled
Bearer: Unspecified
MVNO type : None
MVNO Value : Not set

How to setup Ja Mobil APN Settings for iPhone or iPad?
In your iPhone mobile go to Settings> Cellular> Cellular Data Network> APN and fillup the following information.

Ja Mobil APN Settings for iPhone iPad

Cellular Data:
APN: internet.t-mobile
Username: t-mobile
Password: tm
LTE Setup(Optional):
APN: Blank
Username: Blank
Password: Blank
MMS:
APN : internet.t-mobile
Username: t-mobile
Password: tm
MMSC:  http://mms.t-online.de/servlets/mms
MMS Proxy: 172.028.023.131:8080
MMS Message Size: 1048576
MMS UA Prof URL: http://www.apple.com/mms/uaprof.rdf