Glitch after beating the game

hello i just finished the game on xbox 360 with my lvl 50 soldier and completed all missions except the ones at the underdome im sitting only needing to beat 1 collesium of the smaller rounds and decide to check out online i join a game and it says new mission he was in trash coast so i went out again went into single player and 3 missions showed up that i already completed Claptrap old haven claptrap Crimson fastness i think and talk to tannis so i think ok annoying bug ill have to clear everything from here AGAIN so i try to do so complete one of the claptrap missions the old haven one after that ill complete the talk to tannis in crimson fastness shes in that cell and stuff i go down there and it says completed turn in but it says i have to do it at that cell with noone ind it and i cant click it opne it or anything now i really loved my almost perfect gamesave i almost had every challange as well so please help me deal with this glitch i bought every dlc and planning to do so further on ;(