I hope its sorted as that can be very frustrating. It would be good to know what happens if you text via whatsapp, viber and iblacklist.
Also, to see if its your phone or rather your sim, can you swap sims in your fones? this way you can work out if it your phone or your sim thats causing the issues.
Post back if the outcome is good or bad as your issues could help others with the same problem in the future