Q: information set by the apple shop assistant

Please can you help:

I purchased my iMac computer 4 yrs ago from the apple shop with my mac book pro but for the last 2 yrs it has been asking for my password but i could not remember it so i went to reset it but the information that is on file that the assistant entered does not match my now i cannot complete any update  without entering a password i have contacted apple but never receive any replies by mail can anyone HELP

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