Three.co.uk complaint: Mobile Phone missing While in the hands of the Courier from DPD

I have a contract with Three company for the past 10 years the contract runs on a 24 Months basic, my last contract ends some times this year I have only decided to renew the contract the last part of April. I have requested for an S9 Samsung Galaxy it was delivered by courier on the 30th April, I have set my new phone overnight but by the next day while at work I notice that the phone was overheating when I return home in the evening around .6.30 pm I call three company and explained to them the problem with the phone. I was advised to arrange for a delivery that I need to reset the Phone to factory setting and a courier will pick up that phone and deliver a new one. which I did
I have received an email from Three company to say that my new Phone will be delivered on the 8th of May between the hours of 12.57 to 13.57 by DPD service. THE COURIER WAS ON TIME when he came to my door he hands me the package with the new replacement Phone and took the one I am returning he open the box then asked why I am returning the phone I explain to him my problem that it’s been overheating on my first day. he then places the phone I gave him in the return bag and left.
on the 28th of May, I went into work as normal and ready to used my phone to log in but unfortunately, I was getting any signal I tried making calls but not pop up advising me that emergency calls only. when I reach home I used my partner phone to call Three customer service and after several checks the person I spoke only found out that my phone has been blocked when I asked him why that when he told me that a message on the system said that they did not receive the phone that they have only received an empty box. until that have received the phone they will block the phone I amusing.
since then, I have been running around trying to help what to do.
I have also contacted the police send email to Three company yet up to now I have not received a reply I have also send email to DPD they too have not responded to my email.. one occasion I called and spoke someone in Glasgow. she then turns the phone back on but by the next day, they have to turn it back off. I call again Thursday and spoke to another customer service officer he advises me to go to my nearest Three shops for help. On Friday after work I went to the shop in Stratford and explained to the manager he then call Three and spoke to them they asked to speak to me and to my surprise the customer office said that they did not receive the phone but an empty box and that they have no reason to doubt there partner DPD who have to fail to return the phone. I was very very angry I hand the phone to my wife who was with me at that time the man keeps repeating himself to my wife that they don’t have reason to doubt the DPD driver and team because we did not return the phone. the manager at the shop in Stratford advice me to leave the phone they will return it back to there warehouse which I did because three has blocked the phone