DPD - Lack of professionalism following a major mistake

I was expecting a parcel to be delivered by DPD in September. A comment mentioning that a person tried to deliver appeared on the tracking page even if I was sitting in my shop all day long so I do not know how I could miss it. A new delivery was planned but no news for few days. I ended up calling to get some update and I was told that they could not locate the parcel anymore. I kept calling every second day during a week but the status was the same, they did not where was the parcel. Therefore, I asked my supplier to send me another parcel as I was needing the goods for my business which I received few days later. After 3 weeks, I got a call from DPD to tell me that they found back the parcel, the person asked me if I wanted the parcel, I clearly said NO, explaining her that I already got the goods and she agreed to send it back to my supplier. Few days later, I discovered the parcel in my shop, they still delivered during the time my housekeeper was there for cleaning even if I clearly refused it over the phone. For the past week, I am calling them everyday, spending money as they charge the calls and wasting my time, I am told that someone will call me back which is never happening. I am just fed up by their lack of professionalism after a major mistake form their side, loosing the parcel for 3 weeks.