registrar refuses full access to my domain

[tim84]

hi all

Im really concerned about a problem with a domain reg at namecheap
I bought a domain and website somewhere and the seller sent methe domain to my namecheap account, today after some monthsof the domain transfered, I tried to push the domain to nother account and noticed I couldnt. asked namecheap and they told me that actually the domainwas not pushed atall the first time, instead of that my seller grant mefull privilegies to manage the domain,but it still in his namecheap account, i said namecheap that their system is showing the domain as mine since when i login my account it is listed the in "MyDomains" list however they still say that that is just for the modif grants. Im abl to modify whatever i want for that domain (DNS, nameservers, contact info , and rgistrant info), so basically the domain appears in the whois as MINE, however i do not have rights at namecheap to push it or to transfer to another registrar,
i checked icann rules and found that the person in the whois database is the owner, no matter what namecheap thinks, however they are refusing to help with this issue, i also asked them to block the domain at all until this resolved and they rejected it.

so my question is: im the legal owner or not?
if yes, why namecheap refuses to give me full access to the domain?
if not, do i need to fill an icann complaint against namecheap or the previous owner?

any help will be very helpful, since im not good with law terms
ps. sorry my poor english