This lot are utterly hopeless. If you're a Landlord, don't rent through them (unless you enjoy annoyed tennants, and generally incompetent estate agents).
Haart Residential Lettings, 17 Clapham Common Southside, Clapham, London SW4 (firstname.lastname@example.org email) are amongst the least professional, most incompetent estate agents I've ever had the misfortune to deal with.
I'm a tennant in a flat, for which Haart collect rent. They originally told me to pay rent to the landlord direct, which I duely did. Later, they told me I was in arrears. Of course, I was never in arrears, but they hadn't see the money, so assumed I must not have paid it (and of course didn't ask first). I thought I'd got that sorted out, but it happened again two weeks later, on the day the money left my account. Thankfully the bank was very good about it, and diverted the money to Haart themselves (with the appropriate payment reference). Two weeks later, a very official looking and sounding letter arrives stating I'm in arrears and have to pay immediately. For the third successive time, I'm on the phone to some incompetent loser at Haart, who agrees everything "looks right", so they'll sort it and call me back. For the third successive time, it's (probably) not sorted, and they haven't called back.
I know that mistakes happen, which is why I've been generally pretty forgiving and as co-operative as I can be. However, when a conversation opens with "you're 21 days in arrears", you get pretty fed up pretty quickly. If they'd just checked any of the details with me, I'd have helped them out, and this would have all been sorted. Instead, they come out with guns blazing every time. To me that's incredibly unprofessional. Their inability to sort the situation (which let's face it is about collecting money from someone who's happy to pay it - ie. pretty damn simple) is incompetent. If you can do one thing, it should be collecting the money (not a great business plan otherwise ;-)
Since they've raised the stakes by sending a letter (from the manager), I have to respond with equal strength. The old wordsmith skills were dusted off, and a snot-o-gram was composed. I'm even CCing the landlord, by way of ensuring that all possible bases are covered (I get on well with the landlord, so I'm sure there'll be no problem on that score). Haart will soon regret bringing my credit worthiness into question ;-)
Anyway, if you're thinking about dealing with them, think about going somewhere else, or otherwise get any contracts you sign re-worded to include clauses that give you recourse if they screw up.