The first one sounds high to me, but its not really possible to say without knowing what extra included - 5 years support, additional cable installation at the start could have been included and the rate on the lease could he high (pubs are generally not brilliant for leasing). The original quote would offer better insight.
But the second one is just plain wrong from what you have said. Nothing short of a complete substantial new system would account for that amount extra per month while keeping the old lease running.
I'm not sure on how much recourse you have as these are b2b transactions and you will have needed to confirm with the leasing company you are happy with both the installs before they pay out to the installer(thats how the ones ive dealt with work). Keep on at the original installers until you can speak to them - they shouldnt be ignoring your calls. This only makes sense to me if there has been a genuine error, or possibly a rogue salesperson.
Btw, I have seen some leases that dont include all the items from the original quotes as items - support and software are not physical assets and some leasing companies wont cover them. So the cost gets wrapped up in the till part of it. Dig out the original quotes/correspondence as these will give you a better idea of whats been agreed.
On a side note, if you are still trading and not using the web version of the back-office, get someone to show it to you. Its so much better than the desktop version. Can also be used with the table ordering/takeaway applications to help with the current situations. If you need a different reseller to help you, pm over you details and I'll get some one to contact you. Wont be us, you're a bit far away I think.