Hosted Exchange service - a problem?

I have a client who were getting abysmal speeds on ADSL due to the distance from the exchange.  Virgin are not in the area so Satellite was their only option.  They took up the Avonline/Tooway service about 12 months ago and have been happy with it - far better than ADSL was, for the two users on the system.

They are now looking at migrating to "the cloud" and have (upon my recommendation) moved their email onto a hosted Exchange server with Fasthosts.  This works fine on  their iPhones/iPad but their laptops are being a bit of a headache.

I have setup Outlook on each of their two laptops to use Exchange Server with a cached 'offline' folder.  The upload of their old pst files went fine, although I did this on my ADSL connection at home.

When they are using the laptops at home in their office they always appear to be synchronising one folder or the other and they have frequently advised me that emails which appear on their iPhones/iPad don't appear in Outlook.

I have spoken to Fasthosts support who suggested that it could be a compatibility issue between Exchange 2013 (where the mailboxes are hosted) and Outlook 2007 (running on the laptops).  I have upgraded the laptops to Outlook 2013 and set up new mail profiles and the problem is still the same.  The laptops never seem to end updating folders and some emails do not appear in the Inbox on the laptops that do appear on the idevices.

The weekend I have setup a mail profile for one of the accounts on my own machine (running Outlook 2010) and the mailbox has fully synchronised in less than an hour.

Is hosted Exchange with cached offline folders not possible on the TooWay connection?  Or is there some tweaking to Outlooks settings that can be done to make it work.

If I can't get it resolved then I will just have to revert back to pop/smtp on the laptops - something I would prefer not to do.

Any advice appreciated.  TIA