But thats the point Cat, all delivery companies can be terrible as its generally up to the local depot to enforce good service, citylink here werent the best but everyone else was MUCH better so generally I avoided citylink where possible.
I have probably ordered about 200 separate deliveries from amazon during my 2 year subscription and a fair few of them have been saturday or sunday deliveries, the sunday ones are always DPD and always arrive and the others have managed it without issue apart from a couple which is negligible.
Unfortunately you're in the minority of having a terrible delivery depot for some reason and as terrible as it sounds its hardly like Amazon are going to change their entire delivery contract just to ensure certain areas dont use X delivery service, it would probably cost too much.
For amazon support though as soon as I email them about it not arriving they say wait 1 day and if its not sent then they send another item out for next day which is better than any other company I know, every single business will tell you that it is the couriers fault that they have delivered it within the timeframe they stated because at the end of the day the business (amazon in this case) has been told by courier X that it will be delivered within 24 hours and thats that, if its more than 24 hours then its up to the courier to resolve it generally.
I had an experience with one online store I used and the item was sent via royal mail (very reliable) but it never arrived, they made me wait 12 days as this is the window Royal Mail makes them wait to put in a lost package claim, I got my item after 18 days (someone must have found it...) now that was a joke to me as it wasnt my fault but the company refused to send another one, I decided to avoid that from now on as amazon actually send it out next day if its 'lost' in post.
Vote with your wallet, they use a terrible courier in your area so dont get prime and boycott them and maybe if everyone stops using it in that area they will have to explore solutions to fix it .