UC PAYMENTS CALCULATIONS

I have come to the conclusion that the calculators used for calculating the sum of entitlement are very flawed.
This is where all the overpayments and underpayments are manipulated by UC and they are very guarded about
this flawed system.
What I ended up doing was knowing the ammount of ESA I was entitled to before the switch to Uc that gave me a base figure of what I should be getting and as long as I was not receiving less than what I was previously paid I knew I was not worse off.
The other confusing thing I discovered was that my ESA does not actualy stop as it is only rent and income side of my ESA that was affected by the switch.
I kept on receiving ESA payments and thought they were overpayments it was not untill I phoned the helpline and they explained it was only the rent and income side that was being moved to Uc and I was entitled to the payments being made which was a huge relief as I thought I was going to be in huge debt.
I still can't for the life of me get any honest explanation on the calculations that caused an overpayment that was adjusted twice I was told that because of a rent oversight and a payment that already had been approved in rent and could not be changed as it had already been made. I did not really care about the overpayment as the payment they had made to me covered what I owed so I paid it back straight away. I could say much much more but don't want to make myself a target as I had a few fights with them during the migration process and kept copies of all enteries made in my journal.