VOIPBuster - Can't buy credit

I have been using VOIPBuster for some time now but my purchased credit has
been used up. Now I find that I cannot buy more credit. I just get a message
saying they have sent me a verification e-mail but no such e-mail ever
arrives.
Attempts to get a response from their feedback desk produce nothing but an
immediate auto reply saying they will deal with the matter asap. This has
been the situation for about two weeks. Has anyone else had a similar
experience?

Brian