Credit available got taken away

I am very disappointed by Specsavers Mediwallet. I have been a loyal customer for more than 3years and have never missed 1 payment. I app**** for an increase in my credit which got declined whilst I can afford it and am credit worthy. I can still accept this but then my account got frozen and I am not even able to spend the credit that I had available. I find this unacceptable as this was my balance that I had available and there is no apparent reason why this should be frozen as I am a loyal customer and have been for years. I cannot comprehend that a loyal long standing customer should be treated like this.