No Service, No response

I app**** for a limit increase on my credit card in October 2015 already. Since then I've had no response and have tried phoning, staying on the line for more than 20min at a time without any answer. I've also e-mailed them twice and tried phoning them again just now, no answer!!! And if I go into a branch, they're going to tell me I have to phone the call centre...