Do you not get something similar to this in your area/county?
What do you mean "do you not get"? If you mean "have you not received", then the answer to that is no. (English isn't your strong point, but I guess that's excusable if it's your second language.)
Received by what means? Is that the letter supposedly sent out from the PM? I guess (being in Wales) I might not be on his contact list. However, my elderly friend in England has not mentioned receiving anything either.
Who is it you are invited to contact? Would it be any use? The government show no evidence of joined-up thinking: "Hey guys, here's a great idea, we all order from Ocado so we'll tell the 80+ elderly to stay at home and go online to order from Ocado too". Well, I'm sorry Boris but I have two 80+ friends who wouldn't know where to start, and there's not enough time to set them up and teach them how, even if it were possible to place an order (and if it were possible to do that while social distancing, even if there was any chance they would remember what to do next time).
The weekend before last I managed to get a Morrison's Click&Collect scheduled for the following weekend, but I had to place the order there and then to secure the booking. Some items I wanted to order were shown as "out of stock", so I couldn't order them (but was that based of projected stock at time of picking? I doubt it). However, I was allowed to edit the order until the night before. On the following Saturday I went in and revised the order. Other stuff was "out of stock".
Not knowing how the system worked, I went down near the start of my allotted time (4-6pm) and waited in the Click&Collect parking area. Every now and then a lad came out with two pallet trolleys and went to two cars. It was not obvious how those cars were being identified. Two hours later I received a text and an email telling me my order had been picked, what was missing outright, and what had been substituted for other items (not very happy, but I decided to take what I could get). My order value had gone down by a third.
The text and email contained a link to a web page where I could register my presence and identify my car. How would somebody without a smart phone do that? As it is, I don't have an alert set for incoming emails.
I believe orders were being picked at the time, from shelf stock not from reserved stock, despite me having finalised my order the previous night. Consequently, my order had to be made up from what was left on the shelf after a day's trading, and the stock control system (when placing an order) is utterly useless.
That is why I say it is impossible to self-isolate, ie not to have to set foot in a shop, unless you already have a support network to do that shopping on your behalf (and take a risk on your behalf - I'm not willing to ask somebody to do that).