If you've tried the steps suggested in the previous post, the best option would be to contact our support team or drop us a mail on firstname.lastname@example.org so that we can assist you.
Some steps that may help before you do though.
1. Test your SIM in another device
2. Test your device with another SIM
3. Recreate your APN from scratch and ensure that you have enough data in ClientZone (not capped)
This info will be very helpful in determining what the cause could be.