Homeloan account available balance incorrect - FNB can't do recon to match

Homeloan account available balance incorrect - FNB can't do recon to match Since July my available balance has been displayed incorrect on my home loan. I asked FNB to look into it and eventually requested them to do a reconciliation. FNB has not been able to do a reconciliation to match my total balance. The closest they have been able to get was 30% inaccurate or difference (in my favour!). I am more than willing for FNB to adjust my balance to the latest recon they performed...

They have done the recon about 3 times now it it takes them multiple weeks to do a recon. Since there are so few transactions on my account it really shouldn't take this long. It shouldn't take more than 3 days.

Their spreadsheet that they use is a shamble, with inconsistent formulas app****. There seems to be no quality check on this and even simple logic isn't app****: such as that I shouldn't be able to go into the negative, or that my total balance should be at least close to my actual account balance.

I feel requesting the bank to confirm your balances when you have solid grounds for concern shouldn't be this difficult.

Please assist.