need help or advice - panic mode

Both me and my partner work, we had our son 3 yrs ago and told tax people the truth in what ever they need to know and while on maternity (has not on full wage as many know) they said entitled to child tax. so ok had that and told them when went back to work what we earn etc (as you do) they say now we owe them money coz over paid us. (there fault, as they knew everything).

now im expecting again in 9 weeks and I am so so panicking how we going to cope on maternity there as statuory maternity pay is rubbish, I do not think we will get child tax now has they say we owe them. if we ring they wont be able to tel us what entitled to will they?

anyone been in this situation? how did you cope? also what could we be entitled to?

please help!