I used clay sim card services in London and they were really bad. There were perpetually constant issues with the network. Calling the customer care was equally difficult mainly because it took them 2 days to revert on my email with this concern in a single line that said that they are looking into it. Even on a call, its difficult cos they address the issue only after 10 minutes after putting you on hold. After 3 days of this drama, I stopped using their sim card completely. Gave me headaches than convenience.