No Response to Request

I put in a request to Increase the limit on my credit card on the 29/03/2015 and got an email response that they did receive my request and they will get back to me. After 7days with no response I sent a follow up email on the 04/04/2015 received an email again saying they will look into my request. the contact centre never answers their phones as I've waited more than 10min each call I've made. This is really poor service from a bank I've been with for more than 10years.