Bad customer service from ZANDO

I ordered an item from ZANDO and it was big, I requested for an exchange, my parcel was picked up on the 3rd a week later a guy from the courier company came to my house saying he is here to collect the parcel for exchange. I told him the parcel was picked up on the 3rd of May. Every time I email the customer service they send me an email back saying they’ve sorted out my query when they haven’t. Today I phoned the call center the guy that answered the phone put me on hold for 5 minutes & dropped the call on me.