DHL provides the worse service as a courier company

I enrolled my kids in a UK online school and the books were dispatched to DHL 14 January 2019. On 16 January I got an sms from DHL to advise me to complete a form or call the call center. I called and the consultant requested my email address and my ID no which I furnished. Today I called to enquire on my parcel and I was asked to provide this information AGAIN and that the parcel had not been cleared. I asked why DHL is so inefficient because if their system reflected that they didn't have the details, DHL should've contacted me. I was then told DHL did try to contact me and that I did not answer. This is a blatant lie as no one from DHL contacted me and surely if that was somehow the case why was an SMS not sent to me again? The call center people are so unhelpful and customer service has not yet responded to my email complaint as no one has called to update me on delivery of this parcel even though I informed them that my kids are unable to begin their home school studies. I will definitely complain to the provider in the UK of the poor service from DHL.