Can login but account is READ ONLY

Hi hoping someone can advise as to what is going on here. Had account about 7 or 8 years and am not a big user. Have less than 20 tweets and a handful of followers. Hardly use it much at all. I recently got notified of someone tweeting me asking if they could have my username 2-3 months ago. I ignored them. And then again the same person yesterday. I decided to kogin and change my password just to make it more secure in case this person was up to no good.

After logging in it wouldn't let me change my password all I got was an error message saying:
403 Forbidden: The server understood the request, but is refusing to fulfil it.
I even got sent a password reset email but that wouldn't work either. Now having checked it seems I am unable to do anything on the account at all whether that is send a message, tweet, change profile in any way or change any settings at all. All I then get is a message popping down from the top of the page saying:
Your account may not be allowed to perform this action. Please refresh the page and try again

I have gone to the help page when logged in and in there it says that my account is neither suspended nor is is locked. I have contacted support but all they did was send me a message with a password reset link, but as i said that doesn't work. Besides I am loathed to do that until the account is working unless it locks me out completely.

Any one any idea of what this is or has anyone seen this before? Could this be something to do with the person who wants my username.
I even tried to report the issue here
https://support.twitter.com/forms/feature_report?feature=profile
I select the something else option and fill in the report in under 500 characters and all it does is block the submit bottom with a red no entry type symbol. This is madness!!
Any help here appreciated.