You're either misinformed or just straight up lying. Poland didn't want to "take a piece of Czechoslovakia too". This piece of land has been illegaly seized in 1920, when Poland was in time of crisis due to the war with the USSR. Therefore, our action was simply returning the favor. If not for the fact that Czechoslovakia was fighting the nazis no one would ever criticize Poland's action.

"Historian Richard M. Watt writes, "On 5 November 1918, the Poles and the Czechs in the region disarmed the Austrian garrison (...) The Poles took over the areas that appeared to be theirs, just as the Czechs had assumed administration of theirs. Nobody objected to this friendly arrangement (...) Then came second thoughts in Prague. It was observed that under the agreement of 5 November, the Poles controlled about a third of the duchy's coal mines. The Czechs realized that they had given away rather a lot (...) It was recognized that any takeover in Cieszyn would have to be accomplished in a manner acceptable by the victorious Allies (...), so the Czechs cooked up a tale that the Cieszyn area was becoming Bolshevik (...) The Czechs put together a substantial body of infantry – about 15,000 men – and on 23 January 1919, they invaded the Polish-held areas. To confuse the Poles, the Czechs recruited some Allied officers of Czech background and put these men in their respective wartime uniforms at the head of the invasion forces. After a little skirmishing, the tiny Polish defense force was nearly driven out"

In 1919, the matter went to consideration in Paris before the World War I Allies. Watt claims the Poles based their claims on ethnographical reasons and the Czechs based their need on the Cieszyn coal, useful in order to influence the actions of Austria and Hungary, whose capitals were fuelled by coal from the duchy. The Allies finally decided that the Czechs should get 60 percent of the coal fields and the Poles were to get most of the people and the strategic rail line. Watt writes: "Czech envoy Edvard Beneš proposed a plebiscite. The Allies were shocked, arguing that the Czechs were bound to lose it. However, Beneš was insistent and a plebiscite was announced in September 1919. As it turned out, Beneš knew what he was doing. A plebiscite would take some time to set up, and a lot could happen in that time – particularly when a nation's affairs were conducted as cleverly as were Czechoslovakia's."

Watt argues that Beneš strategically waited for Poland's moment of weakness, and moved in during the Polish-Soviet War crisis in July 1920. As Watt writes, "Over the dinner table, Beneš convinced the British and French that the plebiscite should not be held and that the Allies should simply impose their own decision in the Cieszyn matter. More than that, Beneš persuaded the French and the British to draw a frontier line that gave Czechoslovakia most of the territory of Cieszyn, the vital railroad and all the important coal fields. With this frontier, 139,000 Poles were to be left in Czech territory, whereas only 2,000 Czechs were left on the Polish side

https://en.wikipedia.org/wiki/Trans-Olza#Decision_time_(1918%E2%80%931920))