Contact Hotpoint directly. Ask them to supply the spare part. If they supply you then you can get your Fridge repaired.
If they tell you that they cannot supply the part, state that your repair technician has been waiting on this part for 3 months and in that time the part has not been available.
Submit a formal complaint to Hotpoint stating that they have been unable to supply the spare parts for 3 months. State that you have been deprived of the use of your Hotpoint fridge for 3 months and that you are seeking a full refund or a replacement fridge.
If you are unhappy with their response, tell them that you are takeing your case to the small claims court.
Manufacturers are required to provide spare parts for their products for a reasonable time period. Not providing spares for a 3 year old fridge is not reasonable.
I had a similar problem with a slightly over 2 year old Electrolux oven. The glass door broke last January due to a household accident. I tried to order a new door from Electrolux's on line shop, but it was showing as "available soon". I set up an automated notification for when the door became available. 3 months passed and still no door available. I phoned Electrolux and was told it would be available on 3. to 4 weeks. After this period still no door available. I sent several emails complaints and made phone calls to Electrolux and was given a string of delivery promises, all of which were not honoured.
During this now almost 6 months period I asked for a refund or replacement and these requests were refused.
Finally I told them I was taking my case to the small claims court.
Miraculously they then managed to source a door from the UK and as a gesture of goodwill, supplied the glass door free of charge.
To date this glass oven door is still showing as "available soon" on Electrolux's on line shop.