Student or Learner
Please correct the following lines.
As your customer, I would like to know what action you have taken regarding my issue. Because there was no appropriate response from the manager.
Many thanks in advance.
I assume you have already been in touch with this company so I can't see any need to start it with "As your customer". I would suggest something like "With regard to my complaint dated [date], please tell me what action you have taken/you will take because I have not received a response from the manager, [manager's name]".