Apologies. I was almost certainly not 100% correct about them assigning you a new number. It looks like that is (/those are) extra. From the localphone site that I see here in the UK:
"Incoming Numbers lets you rent a number that's local to your friends and family then forward it to your phone. It means that your loved ones can call you for the price of a local call."
As to those different numbers for each contact:
"For each contact you add, we give you a local rate number that will connect directly to them."
and
"Local Numbers allows you to connect straight through to your friends abroad using local landline numbers."
Can you see
https://www.localphone.com/help which would answer these questions.
As to why you cannot make a payment, I found this on their site:
"If you are attempting to add credit to your account using Internet Explorer 11, we have been made aware that there is a compatibility issue for some people. We ask that you please use a different browser to add credit to your account if you experience this issue until it has been resolved. Thank you."