Overcharge on building insurance

In March I discovered that I had been overcharged on the insurance on our home for years and after an evaluation, Std Bank Insurance confirmed that the value of the property had been incorrectly inflated annually. They undertook to reimburse the overcharged amount after I had been charged double the amount I should have been paying for years. I was informed that it would take approximately 21 days to complete. It has now been almost five months and still they have not reimbursed me despite numerous promises and apologies that the matter had not been attended to. They are very quick to take ones money but it is impossible to get what is due to me. Should I see an attorney or what else am I to do?