if this does not work use the internet like Twitter or Facebook
At May 2019 the current number to contact SP is 0800 027 0072
It's extremely difficult to find this out from the website - deliberately so, I'm sure.
The other incorrect numbers on these community posts should be deleted - so perhaps the SP moderator could do that, though I'm not holding my breath :-(
If you call the number above, you'll need your account number handy. Rather than wait on the line, they offer a call back system :-)
However It takes about 3 mins to get through to the point where you're offered a call back. Then you have to enter your phone number and they repeat it back - another 90 seconds or so. So allow 5 mins just to get into the call back queue. Enjoy...
You are correct that is the number when calling from the UK. The other numbers in this thread were for making contact from abroad because the 0800 number does not work internationally.