PDP authentication issues

[Sals15]

For the past week i havent been able to get any 4g - my iphone says its a PDP authetication issue. When i check signal online it says there is a mast down but i have had no further info. Ive tried resetting, airplane mode off and on etc nothing has worked 

[tonyl2]

Me too. 
pdp authentication failure. 
no mobile data for 2 weeks. 
Escalated to highest technical department. 
All I got was a text saying there is no problem. 
absolutely disgusting. I am a TV, broadband, mobile customer for 19 years. Not for much longer. 
Sky: get your act together. Clearly, many customers are complaining of same problem

[tonyl2]

Possible solution:

Provided that your phone is network unlocked, insert another network provider's sim card in the phone.

Power off and on again. The new provider should be recognised in your mobile settings.

Turn roaming on, set to automatic.

Remove the sim card and replace it with the original Sky sim card.

Turn off wifi and then see if your mobile data works.

It worked for me. 

Speculation only:

My pdp authentication problem started after I got back from overseas. Roaming had been switched off while I was away. On my return, I had no mobile data. It's as if the sim thought that I was still abroad.

Maybe the act of inserting a sim from another provider then reverting back to the Sky one has triggered something. Anyway, it's working now. Who knows for how long.