FFW wants me to pay for their mistake.

i insured my phone with them last year together with my house belongings, they claimed they phone costs R8000 which was correct. when i removed house belongings and only insured the Phone, i was told it now costs R4000 i asked how can the value depreciate with half the amount in one year but the consultant insisted and they promised to give me the same phone should anything happens to my phone. when i claimed their hey told me my phone was under-insured there fore i have to pay an extra R2800. this is a mistake done by their consultant not me why should i pay for their own mistake. they are now running away from me. no one wants to explain to me when i call. have sent them tons of emails but no one is responding from the people i have spoken to (CCed on the email).