1) Any unregistered lease agreement is construed as "Month on Month" Lease agreement as Section 107 of the Transfer of Property Act, 1882 provides that a lease of immovable property from year to year, or for any term exceeding one year or reserving a yearly rent, can be made only by a registered instrument.
2) Since your lease agreement is not registered, you can take umbrage under section 49 of Registration act.
3) By virtue of Section 49 of Registration act , you are at liberty to rely on the unregistered lease deed to prove your character of possession which is the Collateral purpose to the terms of the lease deed
4) Section 49 of Registration act does not bar reception of an unregistered document in evidence by Courts for proving possession of property by you and also the claim of you asking for repayment of Upfront amount along with interest.
5) Your claim for refund of upfront money paid by you and also claims for Interest, Damages, costs etc will 100% succeed by virtue of the
A) Unregistered lease agreement highlighting the fact of of you being in actual possession and
B) Acceptance of rent by the landlord.
You should file a suit for injunction against your land lord restraining him from interference in possession of your property till such time the Upfront money is refunded back by him coupled with interests, damages and costs.
Hope this information is useful.