Can I ask for an extension from my ”enter to leave” stamp in the UK?

I arrived to UK on 19th December 2020, and at the border control after the general questions that why I came as a visitor she asked me for a return flight (It was to Italy for March 2021)the officer told me that I was allowed to stay until the day of my return flight and that was given a week extra in case my flight was cancelled and putted a stamp in my passport that says ”Enter to leave until 11th march 2020” and down below the entry 19th dec 2020. So the date was wrong!

Now due the circumstances with covid Im not travelling to Italy because they dont allow visitors, I want to stay longer in the UK until measures are relaxed to travel… Im argentine and dont need a visa for UK and i’m supposed to be allowed for 6 months as a visitor. So I call the immigration office and he just said ” that stamp is irrelevant because you can stay 6 months here that means until June, and the stamp date is actually wrong” But I dont want to be in trouble in the future…Does anyone now if its actually possible to extend this date that I ve been allowed to stay? Someone with this experience? Or knowledge to advice?

Thanks in advance ­čÖé