The EU is mainly complaining about insufficient duty/tariffs - the VAT is a secondary issue.
The EU is simply behaving in its usual protectionist racket mode - it is unable to compete with China in the production of cheap clothes so it applies a tariff to inflate the price of such clothes to nearer the price they can be made for in the EU.
If I buy a cheap Chinese T-shirt, I pay the manufacturers maybe $1, the shippers and handlers another $1, and then the EU wants me to also pay another $1 to them to be wasted by the EU bureaucracy.
Once we've left the EU we'll get the benefit of cheaper clothes while our European neighbours will continue to hand over their hard-earned cash to Brussels.
And you wonder why the majority voted to leave.