The Tanzanian representatives, alias Yanga, bowed out of the competition after losing 1-0 in the second leg of the first preliminary round on Sunday evening.
Substitute, Uche Onwuasonaya, netted the winning goal for Rivers United FC men nine minutes from time.
Yanga lost 1-0 in the reverse at Benjamin Mkapa Stadium in Dar es Salaam to tumble out on a 2-0 aggregate score.
Bumbuli believes Yanga should have been given up to three penalties in the first half.
He was left furious with decisions made by the match officials.
Bumbuli revealed: “We could have killed the game very early but the officiating was biased against us especially in the first half where we had like three clear penalties that were denied.''
''That is water under the bridge. We have gained valuable experience.”
Speaking after the team arrived in Dar es Salaam, Bumbuli also slammed their hosts, claiming that they had a fixed agenda.
Bumbuli disclosed: “We have learned vital lessons in such games especially concerning COVID-19, our counterparts came with a malice agenda. They could not prove the COVID-19 results.”
Four Yanga players were said to have tested positive to COVID-19 barely one hour before kick-off.
The move was contested by the club officials as dirty tricks aimed to distract them from focusing on the game.
In the first leg, Rivers United FC accused Yanga of employing dirty tricks when six members of the former were said to have tested positive to COVID-19 barely two hours before kick-off at the Benjamin Mkapa Stadium.
After falling short of their expectations, Yanga will now seek redemption in the domestic league scene on Saturday when they take on age-old rivals Simba SC in the Community Shield.
The tie serves as the curtain-raiser to the 2021/22 Mainland Tanzania Premier League season.
Yanga will open their league campaign with a tricky fixture on the road against Kagera Sugar.