But the problem was that at that time, relations between Britain and Russia were not good; what seemed to be a letter reminding the Russians instead made Stalin himself believe it was the British trying to sow discord between Germany and Russia.
Why did Stalin think so? Because long before the outbreak of World War II, the British and French had repeatedly tried to sow discord regarding German-Russian relations and even attempted to divert German attention toward Eastern Europe, initiating a conflict between Germany and Russia.
But at that time, Germany was not foolish; most of the Germans' hatred was directed at the French, and to rashly start a war with Russia would have been trouble seeking trouble.
Moreover, Russia, constantly ostracized by Europe, also thought of keeping a low profile, so the provocations from Britain and France had no effect and only made their relations with Russia even tenser.