I have had this problem. I have been in touch with my phone company. They were very helpful . My attemps to top up are not registering and they dont know why so they are contacting their supplier and will get back to me.
I had problems trying to top up my new phone number. It kept on declining my card citing a sercurity reason . I tried my credit card and it refused that . I tried to top it up on the phone but they said my bank had declined payment. I spoke to the credit card company who they had not declined anything on my account. I have contacted the phone company who are going to look into it.