My first check would be on "infantry toughness" in the preferences menu, to ensure that you have not inadvertantly managed to raise this to a high value?.
Shooting at infantry sections at 1 hex will chew them up, but if you have moved rather far, remember that the game will determine your movement as well as any of his, but even so you should be seeing 70% to-hit chances. A couple of blasts from your dismounted panzer greneadiers should make them retreaeat.
If you are really sure there are no units around at pinned or lower - enter the same hex as the target with shift key and really give them a toasting. Especially with infantry as 0 hex combat is melee, and you will see extra casualties from the hand to hand combat.
I cannot recall if MBT has the surender code that is in WW2 yet - routing units will test for any enemy in the next or same hex, and may well surrender to these esp. if these block retreat, and/or there are a lot of enemy units in good morale within 1 hex.
And finally - your infantry will shoot at retreating infantry, in his retreat phase. Dismounting riflemen as a barrier to his retreat direction is good for sweeping up retreating remnants as they retreat
into the firing line. But this has to be done with care - as exactly the same can happen to the blocking line if there are good status enemy about
!.
But with those sorts of reported low results v infantry, I would first have a look into the "infantry toughness" level in the preferences screen to see if maybe you have managed to raise this somehow?. Also - check the other preferences for hitting, troop quality etc, as you may have changed these from the defaults ??.
Cheers
Andy