Hi and welcome to the forum even though I am sure it is not a place you want to be.
I can't give you any medical advice and hopefully one of the more experienced members will provide more feedback. However I do want to reassure you and hope you won't worry.
It is shocking that you can't rely on your GP to follow through on instructions and ensure the correct appointments are made, but I think this is all too common these days and you have to rely on yourself to push forward with the treatment.
I would trust the oncologist's view that all will be ok. It may be helpful to others in giving advice if you post more details about your husband's diagnosis - Gleason score, psa etc.
From my husband's experience and from what I read on here, there are often delays in treatment. However most prostate cancers can progress slowly. My OH was diagnosed in May 2013 and did not have any treatment until Surgery in October. Scared the hell out of me, he was put on casodex in January for 2 years and then started RT about March. Thankfully psa is finally undetectable. It is interesting that people have different treatment plans depending on where they live too.
I know it is a big worry but you need to stay strong and positive, this will get you and your husband through this. Trust the professionals especially the oncologist and keep an eye on the gp appointments, you need them all on your side although it is understandable that you are worried.
Hopefully you will be able to get some peace of mind next week at the review