Has BT limited my internet usage as I have not yet bought fiber

[Backtothere]

I had Fiber Optic Cables installed nearby and now my speed is 4 times slower on average and drops out every 30 minutes I believe this is a trick to try to get me to purchase a BT service even though I am on a provider other than BT.
Is this legal? and is there any way to get around it until I decide on a new provider to run Fiber on.

 

[i7Baby]

Do a Speed Test - google it. Then talk to your ISP if you're not getting what you've paid for.