Roca India / Parryware — Replacement of parts of flush tank

Address:

P.S.chellappa,102,Prasad St, Seethapathy Nagar, Velachery, Chennai 600042

Water from toilet Flush tank started leaking. So I called customer care.
Sometime back one service person came and said that s unit in the flush tank has to be replaced and it is not available.
I purchased one set of internal parts along with my toilet set, as advised by salesperson at that time, when I was working in EID parry
To day, service person Mr.Gokul, who came to my house said that internal parts have to be changed. I told him that I have genuine parts purchased from Parryware.
He refused to replace the parts.
He said that they will supply the parts and fix only those parts.
I have original, genuine parts purchased from Parryware. with Parryware seals.
I don't understand as to why the service person refused to change parts from Parryware.
I suspect that this is a scam to cheat the customer that they will only supply parts and fix those parts only, though the parts I have also are also original.
Is there any instruction that customer should not buy parts from Roca Parryware and those parts should not be fitted.