New iPhone sending duplicate text messages - Resolved

Posting as a potential solution to an annoying problem. I was experiencing the issue already reported by many people where my iPhone was sending duplicate text messages to everyone, regardless of whether it was an iMessage or SMS. This really started bugging me and I called my operator and luckily they were able to help.

My problem was caused and resolved as follows:

• I bought a new phone from a new, different operator to my current one.
• I was given a new phone number by the new operator which I didn't want to use, I wanted to keep my existing number.
• Therefore I transferred my old number over using the PAC code provided by my previous operator.
• Everything worked fine apart from the text message duplication issue which started right after this.
• It turns out that my iPhone was still using the 'new' number (which I didn't want) as the 'main' number on the new iPhone itself. This must have been set by the new operator.
• I had to go to Settings - Phone - My number and manually change this to my old, transferred-over number.
• Clearly when my existing number was ported over from my old operator to the new one, this value remained unchanged on the phone itself and had to be manually updated.
• After this, no more duplicate text messages sent! Result!

Hope this helps if anyone else is experiencing this problem. As many have posted before, there are variations of the issue which all result in duplicate messages being sent, but at least for this scenario the fix is to change the iPhone number to the correct one under Settings. Simple, but only if you know to do it!