Our child is british born but i was told , by the tax office, we couldnt claim child tax credit because of my husbands status. There was a lot of debate on a thread on here but to be honest i gave up because it seemed too much hassle. Groan.
As long as you are a British citizen, then you can claim Child Tax Credits for your child if your joint income is low, something like below 26k. Tax Credits must be in both names as his income is counted too to calculate your claim and it is fraud to claim as a single parent. You can't take extra benefits for him (via the Worklng Tax Credit part of Tax Credits) as he is subject to immigration control. You used to be able to, but from a link someone put on here a while ago, that has been stopped. Does he have a NINo? Ring them again.
It's all changing when Tax Credits is replaced by the one income based benefit called Universal Credit. You having a property you don't live in, might mean that you can't claim UC. You will need to read up on that. UC might already be in in your area for new Tax Credit claims anyway. All you can do is ask Tax Credits about a claim, again. Keep copies of all your correspondence and proof of posting. Make sure they know he is subject to immigration control.
If you earn less than 50k - 60k, then you can claim Child Benefit too, but that must be in your name only as he is not allowed public funds. CB is one of the benefits that gives a credit towards your state pension if you don't work/don't earn enough to pay NICs.