Invoicing early (to get paid early

In message , " snipped-for-privacy@googlemail.com" writes

As you are not happy with their work or their billing arrangements it would be best if you just let them go asap and found someone else but it looks like you have no choice but to continue for the next six months or so in respect of the annual contracts that were paid up front unless you want to write that off. It just shows the folly of falling for such an arrangement.

As for billing monthly in advance that can mean whatever people choose as it is loose enough to be correct with billing on the first, the last or any other day during the month before the work is due. As the annual contracts were paid in advance it sounds like that is their normal mode of operation so it would be difficult to argue against paying early especially if the previous bills have been settled on that basis.

I have never paid for IT support in advance although it is not unheard of and I can understand them wanting the money as soon as possible to ease their cash flow position. It should be acceptable for them to bill on the first of the month with payment on the last day of month after all most companies don't bill until the end of the month in which the work has been done and then give 30 days but as they have been paid in advance for several months they understandably think they can get away with the same thing going forward. You can express your displeasure and see whether they are willing to change especially if they can see the contract ending if they don't accommodate you but it doesn't sound as if you will get far without some leverage unless of course you just sit on the bill and let them walk away. It really depends how strongly you feel about it and how far short of standard you think their work is falling.

Further investigation? You say to them I don't think you did a good job because .... and see what their response is. You have a problem with IT support and you don't have time to deal with it?