The people you speak to are a helpline, & for anything like this they have to pass details to another part of the tax credit office. It should be sorted out eventually but can take time. If your husband is employed (rather than self-employed) they can get the actual information from HMRC tax records. If he is self-employed they will probably ask for more information - such as his annual accounts.
If you get into a real problem - such as they tell you the figure you gave has to stand - there are various things you can do, but you must not accept whatever they say if it is not to accept the correct figure. You can go to the local CAB for advice, or you can make a formal complaint to the Tax Credit Office, or you can ask your MP to get involved. Hopefully, none of this will be necessary.
So far as tax credits for this year are concerned you need to contact them and give them an estimate of anticipated gross income for the 14-15 tax year (for yourself if you have an income, as well as for your husband). If the estimates mean you are still entitled to tax credits they should start paying them again based on the current year's estimated income.