Suddenly we get errors connecting to our Payment Gateways

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PHP Warning: fopen(): php_network_getaddresses: getaddrinfo failed: Temporary failure in name resolution in
PHP Warning: fopen(http://quote.yahoo.com/d/quotes.csv?...&f=l1&e=.csv): failed to open stream: php_network_getaddresses: getaddrinfo failed: Temporary failure in name resolution
PHP Warning: fread() expects parameter 1 to be resource, boolean given in
PHP Warning: fclose() expects parameter 1 to be resource, boolean given in
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These errors show on Custom Files.

Our host says there is no error with Curl.

What can we do ?