Unable to change any billing information

[#1]

Every time I try to change the payment method or even the billing date, originally tried 2 weeks ago and thought it might be because payment hadn't been taken yet, payment has gone and is cleared, so not sure why it's still happening. I get the attached error. Any ideas? 

[#2]

Looking into this, would you be able to try clearing cache & cookies in the web browser and/or try opening the window in private browsing mode (incognito, if you use Chrome)? Let me know how you get on.

[#3]

Hey Gandalf, 

Tried both suggestions and from my tablet, still get the same error, unfortunately. When I click the 'change payment method' option it takes a good 30 seconds to even load up the options. 

[#4]

Hey, ah thanks for giving that a go. What web browser & device are you using?