Attitudes and entitlements changed after I got pregnant: ask the expert

I have been on a maternity cover contract for 14 months. The girl is not coming back and has resigned (she is now launching a tribunal against them for indirect sex discrimination related to her pregnancy and flexi time rights),  a process which has so far taken over 4 months. My original contract was until June, and when the woman didn’t return I kept being extended for 1 month at a time. I then fell pregnant myself, and am currently 7 months pregnant.  They kept assuring me they would extend me until and through my maternity leave, and this week I finally have my date of maternity leave and they said they will extend me until and hopefully beyond then and I’ll quality for full maternity. The term of the enhanced maternity is this: If you have worked for us for one year at the 15th week before your baby is due, you will be entitled to the following:   13 weeks at full basic salary (or the first  6 weeks at statutory if  higher and then 7 weeks a full basic salary) followed by  26 weeks at the Statutory standard rate of SMP.  At my initial job interview, my boss already (I realise wrongly) strongly indicated the woman wouldn’t return and the role would be made permanent for me in the future. Since I’ve become pregnant this seems to have changed and my boss’ attitude has become markedly withdrawn and at times hostile towards me. Now I have had to chase them continually for updates even when my contract was due to expire within 1 week, and have been provided the very briefest of information. HR told me yesterday that after discussion they realised I don’t in fact qualify for the enhanced maternity, as despite clearly meeting the requirements as the policy is worded and was indicated to me previously, my leave date for maternity is actually regarded by them as my end date at the company, full stop. So they see this as not needing to provide me with my full maternity rights. I also wonder how I stand in terms of having being employed on several fixed-term contracts for well over 1 year now, in the same role, that does exist and clearly will still need to exist, but is not being offered to me now the woman has confirmed she is not returning to claim her role. I feel this has all changed since I have become pregnant.  I feel really upset and frustrated and angry this has dragged on to this extent, with me staying in the role after firm assurances I would be given maternity rights and look to be made permanent and now this clearly isn’t happening.