ear buds multi function button stopped working

Using iPhone 5, have updated to the latest iOS (8.4.1) but earbuds multi function button has stopped. Again!
The last time it stopped working the troubleshooting steps involved restarting the phone, restarting iTunes and the computer.

None of those steps have made any difference this time.

I really like the multi-function button and use it frequently. For it to stop working is quite difficult as I must look at and touch my phone to start/stop music, books, phone calls, well - you get the idea. I use that button a lot.

I keep a spare pair of earbuds, but the spare pair is having the same difficulty. So, it may not be the earbuds after all - what else can I do?