... Is there anything else I can try??
Over the past five years I've fitted a lot of tyres, and every time this problem has occured, it's when the tyres were delivered twisted into a figure eight. Tyres that caused least problems were those delivered in a wheel-box...unfolded. Your tyre can be straightened, but it takes a little work.
With the tyre inflated, look around the beadline and mark any sections which are "in" with chalk or crayon. Deflate the tyre and using two tyre levers give the marked section a really good stretch radially outwards away from the rim. Before re-inflating, soap the marked section only. Make a pot of tea and enjoy a cup. Suitably refreshed, and by which time the steel wire beading will have relaxed, it's time to repeat the process. Some of the worst examples I've dealt with have required this process to be repeated four or five times, but they have always run true eventually.
The problem is, when wire beaded tyres are posted folded, the strands of steel wire used in the bead become bent, and can only be reformed into a true circle by the method outlined above. The last five sets of tyres I've purchased online, I've insisted they should
not be folded, but sent in a wheel-box or large bag. The exeption being Kevlar or Nylon beaded "folding" tyres.
I would advise caution when inflating tyres to beyond their recommended maximum to straighten the bead. You can get away with doing this to a 10.00 X 20 truck tyre on a steel split rim, but the chances are, on a bicycle rim the braking surface will flare outwards at an acute angle...and stay that way.