Tenancy rights?

[WitsEnd10]

This may be a long post, apologies in advance.
I have lived in my rented home for 19 years this year, I was a joint named tenant for the first three years, then a sole named tenant for the last 16, although DH has lived here for the last 10 years. My assured short hold tenancy runs September to September, and states that it rolls over for a period of twelve months each September. I rented directly from my landlord until June last year. In June last year the landlord contacted me to state that his son would be managing his properties moving forward. I heard nothing more until August when I was contacted by a letting agent and told that they would be managing the property going forward.
Today I have received, via email, a ‘new’ tenancy agreement to be signed and returned. However it has several clauses I’m not happy to sign at all. It also states that no deposit is held (it is, I have a receipt for it) and that going forward the tenancy is for a period of six initial months and will then roll over monthly. I’m not happy about this at all.
My question is, can this contract replace my existing contract whilst it still has time left to run on it? Do I have to agree to it? Thank you.

In a word no.

Did your landlord/ managing agent move your deposit into a deposit scheme when your tenancy was renewed in 2007. As they were legally obliged to do so when your tenancy was renewed in September 2007

Your assured short hold tenancy falls before changes to the law in 2015, and it seems that your landlord carried the old practice of 12 month roll over after 2018 even though he did not have to.

I don't know the case law so if i were you i would go to the local
CAB or ring Shelter. Don't sign anything without advice

They cannot move to evict you or change an agreement until your tenancy renewal date in September, said just in case they imply or threaten this in the meantime.

Be careful, as if you piss off the son you may not have the tenancy renewed. It shouldn't be like that but it is.
6 months followed by monthly rolling is normal, so I wouldn't make a fuss about that. You can certainly request 12 months fixed term and they might agree since you've been there so long. However they can't replace your existing fixed term without your agreement. Be polite, and say you'll sign a new agreement in September, when this term ends.